The bug doesn't happen when tested in FileMaker Advanced. Only on FileMaker Go.
This bug appears to be 100% reproducible in testing on both an iPhone 6 and 6s Plus.
Once the app gets into the glitched state, no buttons work. The only thing that can be done is force quit FileMaker Go.
When the database is reopened, the records appear normally.
As you can see from the attached screenshots, the blue button bar is also missing in the iphone screen, as well as the customer name at the top.