this is the list of plugins we have, I guess none of them may be related to tags:
I already removed them by hand! or let’s say, I could remove one of the duplicates for each pair; and then the page for the other tag in the pair became in-accessible (even for admins)! as we go to the page, we get “that page doesn’t exist or is private”, though there are several topics with that tag.
an example would be tag یادگیری which should have 488 topics in it, while the tag-page doesn’t exist (link to the tag page):
p.s.: sorry the pages and the tags are non-English. I hope it gives a clue.