I don’t know if I managed to properly fix it, but I looked at the crash log, saw the line “[2015.05.19-17.18.31:402][454]LogBlueprint:Warning: USimpleConstructionScript::FixupRootNodeParentReferences() - Couldn’t find inherited parent component ‘Scene’ for ‘Fighter’ in BlueprintGeneratedClass ‘REINST_Fighter_C_379’ (it may have been removed)”.
So I re-parented the “Fighter” blueprint to a higher parent class and back, it seems to have stopped the crashing.