Thanks for pointing out a solution, worked like a charm for me!
Still, I do not actually know, why this issue happens. I guess, it’s just some bug in this exact version of engine (5.5.x), because I haven’t found any mentions of this error on versions before that, and that happened with me on version 5.5.4
Idk if it was fixed already in 5.6, but if not, someone should probably test it out and file a bugreport to Epic.