@flobler OK, I figured it out already π
This was a stupid typo that I then carried from bed-temperature.g to hotend-temperature.g via copy paste. I tried all these files with PLA previously which worked fine. This time I had PETG loaded but unfortunately looked for PTEG in the object model and not PETG.
Therefore the loaded filament and my bed-temperature.g and hotend-temperature.g system files did not match and therefore not use PETG temperatures before trying to start the print.
Sorry for the noise π