I found the cause. The "--force-device-scale-factor=1" Chromium arg is messing up something when used in combination with "--in-process-gpu". Remove it and check it out yourself to confirm please.
Edit: For some reason putting it as the last chromium arg seems to work. I personally still don't recommend the use of it. Same goes for disabling vsync. It will cause screen tearing and possibly more issues, since parts of the Chromium engine heavily depend on vsync.
(The order of chromium args can also affect how things work. You'd generally want to move more impactful stuff like "--disable-gpu-vsync" for example, to the end of the list.)