Level breaking when opening it from another level

I've been having an issue in my game recently that I have no idea how to fix, when I open a level from another level (for example, when I click play on my title screen. The open level node, y'know), the level breaks somewhat. I suspect it to be a loading issue, here's some of the things that are happening: AI NPCs stay in one place, and gives back an on fail. When loading in standalone, I fall through the world every time, and sometimes on new editor window. A puzzle where you collect items to open a door reports that all the items are already collected when the level is opened, and the blueprints that give some VFX to the spawn blueprint (that makes no sense I'm sorry) don't even spawn in.

This is only a problem when I open the level from another level, if I play the game starting from the level that breaks, it works perfectly fine. Like I said before, I think it's a loading issue since I fall through the floor, and I think the puzzle breaks because all the items spawn in after the first few ticks, which the door relies on to check if all are collected (that parts an easy fix, I'll just take it off event tick and instead call a custom event to fire once all are collected. Actually reading that out now makes me think it wont actually work, either way the issue is still the same).

Even the AI not moving makes sense (I think) if it's a loading issue. The only problem is that I don't know how to solve it. I've looked up the problem a ton, and didn't find anything. I tried to create a loading screen, but every tutorial on it is just making a fake loading screen for some reason. I did use a plugin called "Async loading screen" that I think is a true loading screen, but that didn't solve my issue either.

What's the best way to solve this problem?