Apple - APFS/High Sierra - `tmutil deletelocalsnapshots` not deleting snapshots

I think the least-recent time machine snapshots was corrupted - potentially from some system crashes caused by APFS bugs.

I tried running DIsk Utility's first aid, but that froze my computer for over 3 hours (maybe it ran out of space to work with?) - I ended up having to force-restart.

I solved the problem by running first aid booted from an external hard drive install of High Sierra. It removed some old snapshots. I then was able to boot from my normal drive and run tmutil deletelocalsnapshots... which successfully deleted the snapshots and freed up space

Great solution detecting that the filesystem was corrupt when the normal commands were note working. Also note, you can avoid iterating on the list of snapshots and just direct the system to reclaim space up to and surpassing the limit you choose:

tmutil thinlocalsnapshots / $(echo "5 * 1000000000" | bc) 2

The above command asks for 5 GB of cleaning. I chose the echo math to make it easy to dial up and down without the long string of zeroes getting changed. Feel free to simplify the above command with a number you like that’s larger than your drive if you intend the system clean all possible snapshots.

How to thin your local Time Machine Snapshots on macOS High Sierra