Ooof. This does sound frustrating. I think there’s a delay in the information being added to the search index, but you can speed it up by manually triggering Jobs::ReindexSearch in your /sidekiq page (if you have access to it).
I’m going to try setting one up to double-check. 
(To speed that test up I triggered both Jobs::ReindexSearch and Jobs::DirectoryRefreshDaily, after I made sure my test user had made at least one post - not sure if all those are strictly necessary 
)