I don’t think when you run --cleanup-cache with another command displays anything. It doesn’t display any messages unless there was indeed old cache and it removes it. When you use restic cache --cleanup it supposed to display a message saying how many old caches removed or no old cache dirs found. Also, you may be having this problem because user’s permissions. If you’re using restic with the root account, for example, using your regular user to remove old cache would not work because the cache must be stored in /root/.cache/restic and a regular user does not have access to the root directory. I mention this because this was my case in the past. A little silly on my part but, yeah.
You could also delete the cache directory and let restic re-create it again. I was also using this version and just so you know, you can update to the newest version 0.9.4 if you want.