I'm seeing various UISearchController/UISearchBar bugs too. One example: on iPhone (and only on iPhone) setting searchBar.searchTextField.backgroundColor has no effect. If I wrap the set in a Task it works — until the search field scrolls out of view and back in. Then it once again has the wrong background color. Furthermore, if I use something like .integratedButton for my searchBarPlacement I'm seeing a lot of animation stutters when the search bar button item morphs from a button into a field and, later, from a field to a button. It's a nice idea, but a poor implementation.

I think I was able to solve a similar problem, though my problem was slightly different. The short answer is: use at least a .userInitiated qualityOfService in Catalyst; when the qualityOfService is .default (or below) requests become discretionary when the app is in the background (i.e., inactive). And I think that's where the problem is. For a longer answer, see my response on Stack Overflow.