When editing a post with relationship fields (if search filter has been activated) typing into the search bar for the relationship field will bring up related posts. That works with SearchWP 4.1.5 but with 4.1.7, it always returns no results, even when you can see the post you’re searching for just below.
This occurs by simply activating 4.1.7. Disabling other plugins doesn’t seem to matter. Index settings for SearchWP also don’t seem to matter.
This is not about using SearchWP to aid in the search for ACF relationships (they say you can do that, but I haven’t).
Unfortunately, you would need to contact SearchWP or hope that someone sees your question here who has access to SearchWP.
ACF does a standard search query when you use the search field. At a guess I would say that whatever SearchWP is doing to search queries in interfering with the ACFs queries. But without access to the code of the plugin it would be impossible for me to figure out what that is.