Oh god I am having the same exact problem. I compiled 2 or 3 times my character without problems and at some point it’s going to crash stating Unhandled Exception : EXCEPTION_ACCESS_VIOLATION reading address 0x00000021 (sometimes it’s 0xffffff). UE4Editor-CoreUObject.dll (6 times), UE4Editor-UnrealED.dll (6 times too) saying things about Kismet, Slate USER32.dll. The character blueprint have no construction script and no error in during the compile. Always a green check mark.