Deleted Space Not Freed on Mac Pro/High Sierra

I have a late-2013 Mac Pro, 1 TB of flash storage, 48 GB of RAM and High Sierra 10.13.6.

I keep Drive Genius on the computer and recently it has begun complaining that I don't have enough free space (about 27 GB) on the system drive. So, I began deleting big folders, first one that was 40 GB, then one that was 9 GB.

According the Finder, my free space climbed up to about 29 GB, only 1.92 GB of which is marked as purgeable.

What could be causing this? Why isn't the deleted space translating to free space? It has been about 20 hours since the 40 GB trash was emptied and two hours for the 9 GB. Diskwarrior won't run because it's not yet compatible with APFS. I have run First Aid through Disk Utility. It reports everything on the flash drive is OK.

Thanks for the help!