Editor crashed on level opening via blueprint

Hello everyone,
I have multiples Levels ( ActOne, ActTwo, ActThree, ActFour, ActFive, Finale, Fail), but some of them are making the editor crash when i try to open them via blueprit: i.e. There is a cube with “On Actor Hit” → Open Level “Act Two” as blueprints node.
Now, some levels can open but Act One and Act Two always make UE4 crash.
Note: Every level is playable and works if opened with the editor and not the blueprint

The error pop-up is the following:

Assertion failed: IsInRenderingThread() || IsInGameThread() || IsAsyncLoading() || GIsSavingPackage [File:D:\Build\++UE4+Licensee\Sync\Engine\Source\Runtime\Engine\Private\Materials/MaterialInstanceSupport.h] [Line: 39]

UE4Editor_Core
UE4Editor_Core
UE4Editor_Engine
UE4Editor_Engine
UE4Editor_Engine
UE4Editor_Engine
UE4Editor_Renderer
UE4Editor_Engine
UE4Editor_Engine
UE4Editor_Engine
UE4Editor_Core
UE4Editor_Core
UE4Editor_Core
UE4Editor_Core
UE4Editor_Core
kernel32
ntdll

I added the log if it can help.

Thanks to anyone who has an idea of what the problem is!