That's simply a false alarm, like the propeller not attached message that I and others have seen while the drone is flying 100% normally.
Those things happen occasionally.
You don't have a theory ... you have guesses that are only supported by the number of other people repeating the same guesses.
It's easy to imagine wild guesses explain an unproven large number of alleged mystery crashes over water when you don't...
Remember that APAS is simply a tool to try an help the operator in cases where the operator didn't see some obstacle. But it is always the operator's job to see and avoid. So, if a crash occurs because the drone hits something; #1 it's operator...
Sounds like you're the expert.
Now instead of suggesting things that might cause the issue you are concerned about, get the recorded flight data from some of these mystery crashes over water and find out what actually happened to cause the incidents.