This issue has plagued me for years from time to time and it still hasn't been resolved in FileMaker Go version 16.0.2.
It is hard to explain so I've made a screencast demonstrating the issue which I will send to support upon request.
FileMaker Go 16 (and 15/14/...) sometimes goes into a kind of limbo where the startup script will not fire and no script triggers fire.
So far I have only seen this on iPads. My klients have about 100 users using various solutions developed by me and this issue is reported from time to time without any apparent pattern.
It is hard to reproduce, but it seems to occur when the app has been in hibernation for a while. My hunch is that it occurs after the
(I use 360 minutes for several solutions to not bother the user with another login during a normal working day.)
When the issue occurs, the database opens on the layout it was closed on by the Exit script, as if it wasn't really closed, just paused.
I have found no way to restore normal operation other than swiping up the app, which works.
Closing the file via either the script step or FMGo's menu does not work. Close Window or Exit application has no effect either.
(The file seems to close as you are asked for credentials at once if you open it again, but the startup script and any script triggers will not fire.)
More details in the video.
EDIT. I just remembered something I have thought about earlier, and it seems to me that the issue has occured several times if the database has had "significant" changes since the user last used it. Just another hunch, really.