I have had this issue twice now, the patrol grid described in the radio message / Captain's log does not match the actual patrol grid assigned.
IE: I was tasked to patrol AM5144 (West of N-Irl), but the point where the patrol was triggered was actually AN5144 (N of Scotland). I am seeing the same thing happening with AM21 /AN21.
I only noticed because when being assigned the patrol zone (while in port), you can still see the mission location mark, this is how I found the right ones.
Could this be due to the map mod I am using?
My mod list:
https://imgur.com/a/cy4zL