Artisan Support Roof Problem Snorka and Also Cura

For days, I have been printing parts on my U1 and Snapi 350 Dual using PETG with PLA supports and a support roof, relatively problem-free. So far, I haven’t been able to achieve this on the Artisan. As soon as PETG is supposed to be printed onto the support roof, it only prints in the air… Lowering the Z offset by 0.2 mm makes it print properly on the PLA support roof. Days of trial and error led me to swap the materials: PLA on the left and PETG on the right—after that, printing works without issues.

I’ve made countless attempts over two weeks, with a lot of frustration. How can this be possible?
Z distance to support: 0.0.
The test object now works—I’ll now try printing an actual part. Let’s see.