I’ve had my project crash on load two days in a row now as well.
Cast of LinkerPlaceholderExportObject /Game/Blueprints/Pawn/StealthCharacter.StealthCharacter_C:Weapon_GEN_VARIABLE.Weapon_GEN_VARIABLE_WeaponBase_C_CAT to Actor failed
The work around of moving the WeaponBase blueprint (which is my child actor) out of the project folder got me into my project, and then I was able to move it back and access it.
Here is my begin play set up on my Pawn, which might be useful for reproducing:
I think I had my weapon attached as a child actor for one or two backups before having problems, and it definately appeared after I added a grapple-hook function, which references the PawnReference I set from my pawn to set the players location for the duration of the grapple.