Periods in tags have been disallowed for a while now. You can fix it via the rails console:
ssh in to your server, then:
cd /var/discourse
./launcher enter app
rails c
tag = Tag.find_by_name("circle.yml")
If you want to fix it, take the id returned from the above and substitute it into the ?? below. NEWNAME is whatever you want the fixed tag to be called.
Tag.where(id: ??).update(name: "NEWNAME")
Alternatively if you just want to destroy the tag click the text below, I’ve blurred it as some users have a habit of pasting blindly:
tag.destroy
edit:
Looks like these tags are also broken: