In my data model, I clicked "Refresh Tables Schemas" to refresh for all tables in my data model. It incorrectly told me that one table could not be found in source (I then did Refresh Schema on that ...
Maybe it's just slow and lacking a progress indicator: On another attempt, I got the popup about changed fields after a few minutes.
In my case, my query is slow, so maybe if it's doing "select top 1" that's taking a while. It'd be great to at least get an indicator show that it's still processing.