[CC and Milestones, error code 110-578ef827] Stuck On Loading Screen Sims 4

Have you removed any infant playmat from your mods folder? Because that sounds like the exact error that happens when you do that. (I don't know the exact error in a plain text LE, but in an MCLE it includes 

Exception raised while processing zone spin up sequence: 'Object not found: 0x96068b53' (KeyError: 'Object not found: 0x96068b53'), CategoryID: developmental_milestone_tracker:1100

with the 0x number changing depending on what cc was removed)

I did remove a cc mat I had a while ago

If that's the cause of your problem, it can be solved by either putting the playmat back in and cheating away the infant motor milestones gained by all sims in all households on the playmat (grab seems to be the most common one) (I don't know of an in-game way to do this, but Lumpinou has a milestone cheat mod), or by using Lumpinou's cc/mod object fix to unlink the playmat from the milestones.

Both those mods are free even though they're posted on patreon, and you shouldn't need to keep them in after you fix things. At least I don't think you need to keep the cc fix one, unless you have other playmat cc, then it might be a good idea to keep it.

CM Edit: Do not link to mods on AHQ. 

any advice for if the mod doesn't fix the issue? Or reinstalling the baby playmat.... or deleting my mods and making a new mod folder. I even deleted my sims 4 folder all together, opened the game to let it spawn another and moved my files back in. My game crashes everytime I try to play. I have repaired it I've tried everything no one can help me ☹️

@deerchelsDid you reinstall the same baby playmat and then reload the game? If it's still not loading, it could be that you have a different mod problem, by coincidence.

I have modifications and custom content installed, but even after attempting to load the save without them, the same issue persists. Furthermore, this problem seems to be isolated to a specific family/save, as starting a new game loads without any recurring loading screen issues.

Apologies for the delayed response. But Yes, other households are loading into this same save without any problems.