With the information I have it is not possible to help any further :( That issue (the one in which you have a question with a given tag and clicking on the tag shows no question) does not happen to me. I have to assume it doesn't happen to other users as they would have already complained by now.
I still think there is some issue with a custom plugin. The core does not have that issue.
Regarding the missing accents in tags, that's fine. The core strips them and normalizes the tags