Missing icons in web interface (snap install)

I recently installed nextcloud via snap. Now, there are no icons for apps or files/folders in the web interface.
The interface looks like this:

I tried to repair the cache with “sudo nextcloud.occ maintenance:mimetype:update-db --repair-filecache”, but that did not help.
Another, maybe unrelated, issue is that when I try to change the color in the theming app, I can’t do it. I just get the message “Saving…” which runs forever.
Any help would be great.