attached is a zip of a simplified version of the last comment.
Use BS westpac, Database HCDB2-170909
I used GE vers 2024.003
start with saved game Patrol-good.hpq, where airfield AAa has a group formation patrol of two Hawk, select the base and split off one of the patroling Hawk, enter a new course for the split off AC (eg RTB). Look at the patrol editor for AAa, the patrol notation is now wrong for the remaining Hawk (this is one of the indicators of this problem).
This gets you to the included Patrol-bad.hpq file.
If you let the game play on the hawk in group patrol will run dry and crash.
This is reproducible every time.
This might not be the same cause as in the original post report but it appears to be the same effect.
patrol-good.zip