I have made a pull request so the solved plugin keeps working on stable v2.5.x.
Newer commits will remove the “solved” search option from the advanced search.
https://github.com/discourse/discourse-solved/pull/92
Additionally, I was trying to make this post from this page
and I got the error “There was an error tagging the topic”. I hit F5, went back to /latest and then pressed “open draft” and then “save” and then the post was accepted.