"2018-10-21 02:57:08 - PLAN: Type 041 Yuan is dropping BOGEY #1077 from its target list (Reason: The target is outside the unit's patrol/prosecution area)."
after over 30.000 repetitions and 2 hours game time later I decided to fill bug report

I attached log (problem starts at line 6383 and runs till the end of file). Save game also attached (you need to switch side to PLAN), but after reloading problem stopped.
On a side note, sub shouldn't be interested in plane, especially when its not armed with any kind of AA weapon and its mission is Sea Control Patrol

Edit - version 1.09 RC5