Please help, I updated my project to 4.22 today and it broke my project, the editor is stuck loaded the project at 95% and wont finish loading, I stupidly updated my backup as well as now everything is broken and I dont want to lose it all.
edit: it eventually did end up loading, it just took me leaving it for a good 20 minutes.
I hav the same issue, after the update UE4 is loading much longer and exactly stuck at 93 or 95% for a few min. And it’s after all the build and shader compile, even when I just re-open the editor.
It’s a different case, probably when the editor is compiling the code and shaders.
The issue with 95% and 4.22 is happening every time, no matter if changes was made or temporary folders still in place
I had to leave a project for almost 50 minutes … I would try leaving it for longer. Normally what I do is open Task Manager and then start the process. I will watch some TV and check Task Manager is still refreshing its usage … this normally works for me.
To be honest, this has only happened once or twice to me … but after I have done it, it doesn’t happen on the same project again … unless I deleted Saved, Intermediate, and DerivedDataCache folders.
I have tried to dig into it and found it’s happening because of some Garbage Collector right after the startup map loaded.
GarbageCollector.cpp:1502:
FCoreUObjectDelegates::GetPreGarbageCollectDelegate().Broadcast();
But I have no idea what’s going on 
Update
After further digging, I’ve found it’s happening for the projects which have Niagara Systems in the startap level used (no matter how exactly – directly put into the level or referenced from another objects which in turn are placed in the level or inited some other way on start).
For some reason, UE4 is re-compiling all such niagara scripts each time when loaded, instead of saving it into DerivedDataCache for reuse.
I’ve sumbitted the bug report to Epics, hope they answer soon.
Update 2
Epic guys have responded and told me the bug is already fixed in their internal repository for the 4.23, so we have to ait…
Workaround (partial)
Just create an empty level and set it as a startup map! It starts to load very fast as it should! Though then loading the original map will still be a problem, but I think it’s better anyway.
Hey I’ve added a workaround in my answer, please check it should help while waiting for a reply from Epics to my bug report