Adding DIN-Template to print model invalidates print model

I have an exisiting print model to which I want to add a DIN-Template-print model. I can add the template, but the adapted print model is directly considered to be broken and cannot be manipulated.

Do I have have to start the entire print model from scratch in order to get the DIN-Template in there?

No idea why, maybe the SME had a bad day, but redoing the same steps this morning showed no issue whatsoever. I didn’t store the resulting JSONs from the problem above, so I don’t have anything to investigate why it went wrong. At least I only have to redo one singular segment, not the entire print model.