unfortunately it's not the local backups. I guess the missing disk space is related to the error I get when I check the partition. I guess I need to reinstall... :(
My AFPS volume got corrupted probably during the upgrade to High Sierra. No data lost, but my disk is missing almost half the disk space. See https://apple.stackexchange.com/q/311843/26185
I recently reported a security issue to a quite popular open source project (which has at least some company support). The fix is ready but because of coordinating other security fixes into one big release it is - after almost 2 month - still not released. I wonder if this is normal? What else can you do? Full disclosure?
tl;dr:
- Missing disk space can be related to a broken filesystem
- APFS tooling is currently really bad, you probably need to erase the volume and reinstall to fix any filesystem problem
... and this was in 2018 and I fear not much changed.