Update: the idle CPU usage might be due to the sidebar. After closing it, the issue seems to be gone. I’m using the “SoDaReloaded Dark” Theme.

Edit: No, that was a false guess. Still issues with sidebar closed and default theme.

The CPU usage is quite interesting. It uses around 25% on a single core (3% on 8 cores) for about 5 minutes and then it stops using a lot of CPU with a last peak of100% usage and a memory peak as well: