Hi Silvan,
I could tell as soon as I saw your screenshots that you were running an Intel GPU. This appears to be a driver bug that appears on almost all Intel drivers that don’t support OpenGL 4.4 and above. I’m probably going to turn tessellation off by default for these drivers until I can figure out some kind of way to work around the bug. I’ve been able to repeat this on older Intel GPUs in the office and have made numerous attempts to figure out if there is some way to work around this issue always coming up empty.