I had set up a tariff the other day with a plus sign in its name and couldn’t edit it, I recreated it with an ampersand and had the same issue, I couldn’t delete them either. Upon checking the delete request on inspector in Firefox, I noticed that the characters weren’t url encoded. Editing the request with urlencoding worked. Hoping it may help someone and could eventually get fixed. There may be other data types in preferences and other settings that may be passed with the same problem.
Thanks for reporting this, tariff names with special characters can now be deleted/updated.