Git stash fails 'error: unable to resolve reference refs/stash: No such file or directory'

I was having a very similar issue, after a corrupted filesystem.

The solution was to remove the file or directory at .git/logs/refs/stash

After deleting the file or directory, please use git stash to create a new ref, and that's all.

This will delete any stash you might have, so please be careful.

git stash
error: refs/stash does not point to a valid object!
rm -r .git/logs/refs/stash
git stash
Saved working directory and index state WIP on master: e1d74d8 fixing get_thumbnail_list

I had to delete following file also to get it working.

rm -f .git/refs/stash

You can remove the stash and add new stash folder if the problem still remained after remove the stash:

rm -r .git/logs/refs/stash

mkdir .git/logs/refs/stash