Samsung 970 EVO Plus NVMe not freeing up space after moving files

On my Win10 pc I have an NVMe SSD drive that's almost full with 1.25 GB space left. So I cut and pasted 15 GB worth of files to the OS drive with lots of free space. The recycle bin is empty. Color me surprised when it stayed at 1.25 GB free. Rebooting and completely shutting down my pc didn't work. Any ideas what could be causing this? Hopefully not imminent drive failure...

Note: It's not an OS disk and there are no temp or cache folders that I know of (hidden files are visible and I can't see any).