Somehow tags with hundreds of questions were incorrectly synonymized and merged. I wrote a post on a local meta about this and a moderator unsynonymized the wrong tag. Now the tag that used to be false "main" tag has all questions of both tags and the other tag has no questions. Is there any reliable and fast way to restore the state of question tags to the same as before this incorrect synonymization?
Moderators on the local site don't know how to resolve this efficiently. Their suggestion, to try to distinguish questions by their content using SEDE queries and manually edit question tags, seems to me a slow and unreliable way of solving this issue.
Maybe there are some moderator tools they are missing or this can be resolved by request to Stack Exchange developers?