a short update: I tested to launch a clean project with the 4.20 to my s8 that was not a ARtemplate and the launch just worked like a charm.
So is there any bug with the ARtemplate and the 4.20 version?
I also tried to launch an ARtemplate on the 4.19 but there I get errors too. They are not the same but there is still nothing launching.
Has anybody there experienced those errors in a blueprint project as well?