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