Strange HDD Activity. Any input appreciated.

I have two old SATA drives in an external bay connected to a Windows 10 system. I've been using the drives like this for years with only a couple of small issues in that time. (Corrected using the "Check Disk" feature in the properties.)

The new issue is this:

1/ The volume name of one drive (1TB) changed to match the name of the other drive (2TB). (Drive letters remain different.)

2/ Several folders disappeared (probably 5 or 6) and the space they previously took up is now showing as free space.

I tried checking the disk to correct errors (nothing found). I tried checking the indexing in "indexing options" (no dice).

Any thoughts on what might have happened?

It shouldn't be a virus, as the computer is not connected to the Internet, but who knows...?

Drive might be failing? It has spent many years online, but the disk management application seems to think it's healthy.

I think I have everything that is missing backed up on another drive, so it's more of a nuisance than anything, but I'd like to know what might have happened so that I can avoid any potential issues in the future?