@CaptainNapalm Thank you for the savegame.
Indeed, when I use your savegame the situation appears to be resolved incorrectly.
However I have recreated similar scenarios using the current TripleA pre-release (2.3.21385) on different maps (including BM3). All of those have been resolved correctly.
So there was
a question to attack or not
a question to submerge or not
correct surprise strike execution
That brings me to the following conclusion:
Either there has been an issue with the engine (what I doubt but cannot exclude for sure) but the issue has already been resolved with current versions or
there is an issue with your game that contains some triggers that might have somehow messed up the correct resultion of the situation (what I cannot examine in depth, knowing too little about that specific game).
So I recommend to
install and run the latest TripleA-version and the latest map-version
begin a new game and see if that issue occurs again
Maybe @regularkid wants to take a look into it, too.