Just a user, not a dev.
There is currently an open issue about this.
It seems that this currently occurs because CTRL+F search results are shown only in the viewer pane. So if you are displaying only the editor pane and Joplin didn't show the viewer pane when a search was requested, you would not see the search hits.
There have also been posts in the forum, such as this one, asking that search hits are also shown in the editor pane.
So it's been flagged but I don't know if it will be / is being worked on.