I thought of a solution for the eyelashes that appear solid black with no transparency on 64-bit version for Mac. I don't use Mac however, so I need people to test if it will actually work.
I already made a mod to remove them completely that you can find here. But thought some people might prefer to keep the EA lashes.

This is a super simple mod: Just changes the shader of eyelash meshes from SimEyelashes to SimHair. Just like my other mod, this replaces the LOD0 and LOD1 eyelash mesh files for all ages and genders.

I also have some questions about the issue itself:
Does this only appear in CAS or other places too?
Does this affect all ages and genders or just some?

While testing:
Please check if the EA's eyelash length slider works fine with this mod. (I suspect that it won't work.)
Check how the lashes look in different locations and lighting. Do they look any different from how they do on normal 32-bit version?

Don't forget to clear your cache and remove all eyelash removal mods before testing.

Thank you so much-- the eyelash mod works perfectly with the eyelashes appearing and functioning with the slider as they did with the original Sims 3. To answer your questions about the bulky eyelashes in the Sims 3 64 Bit version, they appeared everywhere. I have yet to check they appear beyond the young adult female age and gender.

Thanks for the feedback! Most people probably prefer to remove the lashes completely but it's nice to have this option working as well.

Hi! I also tested this and it seems to work well. It fixes the blocky eyelashes in both CAS and live mode. Thank you so much for making this!

Re: your questions —
Does the issue only appear in CAS or other places too?
- It appears in both CAS and live mode, as well as in the stylist version of the CAS window. Toddlers are an exception — they have the blocky eyelashes in CAS but seemingly no eyelashes at all in live mode, although I think this may have been true for the 32-bit version as well.
Does the issue affect all ages and genders or just some?
- Yes, it affects all ages and genders.
Does EA's eyelash length slider work fine with this mod?
- Yes, the sliders are perfectly functional.
Do the lashes look any different from how they do on normal 32-bit version?
- I haven't played on 32-bit for a while, so I don't know if I can compare them especially well, but the eyelashes seem a little more... fuzzy? Shadowy? When compared to the 32-bit version. The shadows around the eyes also seem a bit heavier when using this mod. I have screenshots if you're interested.

Let me know if you'd like my device config file — I have advanced rendering off, and pretty much all of my in-game graphics settings are on low or medium, so that might be affecting my experience.