Steps to reproduce
Find a canonical fandom tag that has synonyms, e.g. The West Wing (canonical) and West Wing (syn)
Post a work using both tags
Go to your user page, i.e. https://test.ao3.org/users/USERNAME
Under the Fandoms heading, it shows The West Wing (2). However, if you follow the link, you see there is only 1 work.
What should happen
The count under Fandoms should match the number of works.
It may be helpful to keep in mind when fixing and/or testing this.