eddydenton Said:
"Purgeable space on Data Volume: I emptied the Trash after I put the files there. As you can see in the screenshots above, I'm only using 11.31 GB on the SSD, but the Data volume isn't reflecting this and it seems to be still seeing the deleted items."
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Two Thoughts:
A. Try Safe Mode:
Restart the Mac in Safe Mode (Hold Down the shift key upon boot). Log in, and then restart. In Safe Mode, damages system files (i.e. caches) are fixed. So, boot into Safe Mode, wait 30 seconds, then boot up normally. Perhaps it all needs to sync.
B. Boot into Recovery Mode:
[Hold Down: command + R] upon boot. See what is shown when you view Disk Utility. Is the same shown, storage wise?