SIGKILL is a good way to orphan children. Or end a DB trabsaction without properly closing it (so the server socket stays open, or the transaction lock isn’t released…) It exists for a reason, but docs usually caution against it because it can cause unexpected behaviors.

Kasts is decent. And it integrates with gpodder, which means you can sync with mobile pretty nicely.

Check for mounts hiding the underlying drive?

Sometimes du . -x will help, too. (-x doesn’t cross mount points).