"brian m. carlson" [off-list ref] writes:

It's known that Dropbox and other cloud syncing services can corrupt
repositories.  They can cause files to be removed, renamed, or reappear
after being deleted, and I suspect that's what's happening here.
...
I'd recommend moving the data out of the Dropbox repository regardless,
since, as I mentioned, it is known to cause corruption, and you won't
know it until it's too late.  You may want to additionally run "git
fsck" to see if that finds any problems other than dangling objects.

An anticipated follow-up question is "but then how do I replicate
the repository across my machines? that is the reason why I have it
in Dropbox in the first place", and the above is a hard-to-follow
advice until it has a good answer.

E.g. after finished working at a site, prepare to take the "latest"
to the next place you will work at in a bundle,

    $ git bundle create 2022-07-23.bndl --all HEAD
    $ mv 2022-07-23.bndl $my_dropbox_directory/.

and when you get to the next place to work at, you'd "fetch" from it
into the repository you keep, or you can choose *NOT* to maintain
any local copy there at all and "git clone" from the bundle every
time you restart at a different place.