So I finally got Sims 3 working pretty well. I use some mods and CC and have been careful about what conflicts and what is broken. I use Simler90's Gameplay Core Mod to fix a lot of issues as well. Not using any Nraas mods, since I know some do conflict and some don't. If someone can tell me which ones do work with Simler90's mod, that would be very appreciated. All Store Content that I have has been fixed as well. I've deleted all cache files prior to each time I load up the game.

The issue started when I would exit one world like Midnight Hollow after saving from Edit Town, then try to load into a different world from the Main Menu. The loading bar would load pretty quick then stop about at 99% and just sit there. Music would keep playing as the tips would change too. But the world wouldn't load. So, I would force quit (game doesn't crash), realizing I need to quit the game entirely before loading any new world to play.

Then, if I did load into a world or a previous save, traveling to any of the Worlds, the Future or University would do the same thing. Gameplay is normal, until I send my Sim abroad. Game would load then stop right near the end and sit there, loading and loading and loading away. Not sure if the game froze up but it looked like it was still processing. I did the 4gb Patch Update as well to see if it would help.

I took out all my mods and tested 50/50 each time, also deleting cache files and Current Game files (not sure if it makes a difference after I force-closed the game). If they didn't pass the test, I'd leave them out on the Desktop for further investigation. If they passed, I'd put them back. Then I'd load the game up again and test to see if my Sim could travel abroad. It would work that one time and then have the Loading Screen issue if I loaded up the game a second time.

I'm at my wits end over this. I'm not sure if it's a game issue or a modding issue. I don't necessarily need to have mods that change the gameplay like autonomy, but not sure if some are even affecting the loading for other worlds while still in game. I'm really glad I got Sims 3 up and running again after playing for a couple of weeks until this happened, but if I can't travel to the different worlds in one game or load up another from the Main Menu, I'm not sure what to do. I'm very upset over this and hope someone can help. Thank you in advance.

What you're describing with the loading another save during one game session is an absolute no, it's outright game-breaking. It should never be done, and saving after loading like that may leave permanent damage.
The game does not release resources about previous saves properly and will be using data from the previous load on the new one. It's a certified recipe for disaster- please make sure you always quit the game completely and reboot whenever you want to start a new save or load a different one.

That part aside:
Combining any NRaas mods with Simler's Core Mod is unsupported- meaning if any errors occur, you cannot receive assistance from the NRaas forum itself about them. It's not any specific conflict, but the fact that the NRaas mods contain very many script components that are expecting the EA core + the fact that many of them are trying to do the same thing as Simler's mod. For stability and reliability sake, one should not be used with the other. You are free to use any combination at your own risk, though- it just means it is what it is if you encounter any errors.

Which creates a tricky situation, because playing the game without ErrorTrap and Overwatch installed is fighting an uphill battle. This game can and will run itself into the ground without those mods, especially the more you play.
And for travelling between worlds through gameplay, the EA travel system is also incredibly broken without NRaas Traveler installed.
If you really cannot part with the core mod, those three are the NRaas mods you would have the hardest time playing without.

If you run the game with only your NRaas mods installed and can't recreate the issues, then it's definitely a mod problem. Drag your The Sims 3 user folder (the one that contains the Mods folder) onto your desktop and launch the game so that a new one generates, then test this using that clean folder.
If the issues continue, then that suggests it is something else underlying.

The other thing that stands out is "All Store Content that I have has been fixed as well" - does this perhaps imply the Store content is of a less-than-legitimate origin? It may be in your best interest to ditch it at least during troubleshooting, if so, as these can have all sorts of issues. Their 'fixes' also contain issues of their own and I generally don't recommend using them.
If it's at all possible your game install has a similar origin, that may also be the source of some of the issues occurring.

Ok, well from now on, no starting a new world after going to the Main Menu from a previous game. Got it. Thank you on that note.

I really like and enjoy what Simler's mod does. With that being said, if I keep it and just use Master Contoller with Traveler, would it fix the issue? Not having Overwatch and Errortrap doesn't seem a necessity if I already have the Gameplay Core Mod, as it fixes a lot of issues for the game. Unless they are required.

I will try to see if I can replicate the issue with a test play and see if it occurs. If so, I'll go through the process of resetting the game files and testing mods again.

With the Store content I had purchased, I was having few issues with some of the premium content not working properly. So I did some research and got a couple fixes I could apply to them.

I'll try these steps out and get back to you with an update. Thank you for the help

So I loaded into my last save after making a backup. Got my Sim to travel successfully to Egypt and am playing around a bit. Now, I did install all 3 of Nraas mods: Overwatch, Errortrap and Traveler. Then a few minutes into this session, I get a bunch of script errors.

ErrorTrap catches a lot of issues that would otherwise crash the game, and it + Overwatch clean up a lot of junk data that otherwise goes unhandled. Without them, you would experience save bloat over time and things would generally start to break down along the lifetime of the save. Which is an unfortunate state for the game to be in, not being stable without mods is probably the weakest point of an otherwise incredible game

Many fixes are included with the full NRaas suite, so many that some of them are forgotten / undocumented! This makes it tricky to know whether alternative fixes are needed or not. I play a relatively bug-free game with them, and there's really only one thing I've looked into that only had a fix in Simler's (an issue in the Firefighting career). It may be worth temporarily playing without it to see how it goes, unless you already have specific fixes in mind that you wanted.

The ScriptErrors will write logs to your user folder that can be opened with Notepad, but the contents may not always be intuitive.
It's possible they're simply reporting on cleaning up some of the issues that were around while ET wasn't installed, but it's also possible they contain important information about what is broken.

I see that you already took the logs to the nraas site, which is the right place to go! I'm over there too, so you can respond to this over there if you'd like
But as pointed out there, these logs are unsupported if they happened with Simler's mod installed. If you recreate the issues without it, please feel free to upload the new logs! You can always add it back afterwards and continue to play with the experimental combination, if the issue is fixed / not being caused by it.

I also think it would be a good idea to ask over there about fixes you wanted from the core mod, and those familiar with NRaas will be able to let you know if those fixes can be found elsewhere

Will do, Thank you again for your insight Will report on either site with an update.

That's what I used. Thank you!!

Please don't attach other peoples mods to your posts- and especially not ones that have been modified for pirated versions of the game.
OP already ruled out this being caused by illegitimate Store content- which is what the issue you are describing is caused by. KT's Decrap_Fixes causes the buydebug freeze, and outdated versions of the other fixes (circulated often with pirated Store sets) cause the 'corruption' freezes.

I've download store fixes from other place which works better that these but I lost them a while ago for some reason, so I downloaded the fix from this site. I know that the mod is not mine but I wanted to help somehow

I'm sure that I prevously download them from a Reddit forum page but I can't remember how the title is. Is there a page where we can download working store fixes?

just google games4theworld the sims 3 store fixes. not going to put link since it's illegitimate to post pirate sites

There is a thread where they duscuss about these store fixes from game4theworld here on MTS: https://modthesims.info/showthread.php?t=663649 . The problem is that these "fixes" are working but they cause infinitive loading glitch after using the buydebug cheat or after certain point during gameplay. I was trying to say that I found a year ago store fixes that are working 100% without this bug but I accidently deleted them and I can't find them anywhere.

odd that I've used the fixes but never encountered infinite loading glitch. though I still have one more fix but the site is already gone. the name is fix_juli2014.rar, wonder if it was the same thing you looked for? or else, you can follow this guide I bookmarked last year.