I recently installed 10.3 with all the updates to 10.39, and i'm having a recurring problem I never saw in 10.15, which goes something like this..I create a folder on my osx volume, drag some files into it, and the next time I check, they're no longer there..I just lost over 400 megs of backup files this way yesterday, dragging them into my newly created backup folder, as well as other files inn other new folders..They truly appear gone, that is, if I boot into 9 i cant find them either..I've been getting other weird and unacceptable behavior in 10.3 as well, such as wildly inaccurate file size reporting, but the losing of files is by far the worst..and entirely unacceptable behavior for *any* os..
Anyon4e know what's going on here..it's a very new install, around a week,so it hasn't had a long time for corruption to set in...Anyone? aaaaargh....

Have you booted from the CD/DVD and run Disk Utility?

Also repair permissions (do this from the Finder, not from
the Boot CD/DVD).