Ive had a similar situation happen to me N'W of Lowerstoft.
There I managed to creep between the escorting Armed trawler and the merchant whereby I fired two torpedos and sank it. (the merchant that is)
Then the Armed trawler came looking for me did a fair job and came close, droping depth charges however they missed. He mad about three or four runs then he just parked up and sat there?? When I used the external camara to have a look at him, as I was curious to see why, I noticed they had run out of depth charges. There were no more on the decks and the crew were gone.
I think that perhaps the trawler had reached the end of its escort run and due to the limitations of the game had just stopped where it was?? :hmm:
When it comes to my game and my career I will just assume they stopped to pick up survivors, thats how I like to look at it.
Its only happened to me once, it was around Sept 1939, AN73'37