The "Update Tag Filters" troubleshooting option (available only to admins) uses Tag#synonyms, which generates an error if the tag is not canonical and doesn't have a merger. It should use Tag#mergers instead, to make sure that it works for all tags.
Log in as admin.
Find a tag that's not canonical and has no synonym set.
Go to the tag's Troubleshoot page.
Check the "Update Tag Filters" option.
Make sure that it returns a success notice, instead of a 500 error.
For the next tester use
I tested using the tag ‘DVR’ which didn’t appear to have any syns and didn’t seem to be Canonical. After following the steps, it successfully returned “Tagged items enqueued for filter updates.” instead of a 500 error.