meanwhile i could find the root cause. I didn't mention that i am using User-Defined-Primitives. The G3dMesher Error occurs once a UDP is in the model (even when it is declared as Non-Model!). With the help of the support we found out that this is a bug which was fixed with the 2020R1 Version. Currently my Cluster runs on 2019R3, but this will now be updated soon. I thought maybe this information could help someone else.