Dead fish in the water - Red subs do not navigate

Playing HDS2 3.0, Convoy Ho!, red submarines were painfully hard to detect, yet they were themselves very passive.
I checked what are they up to with Show All.

Looks like there is a some problem, either with the scenario or with the AI navigation, SE shows red groups would need to do creep speed on their patrol routes, except perhaps ZKU, starting from further North at 25kts, but ZKU would also slow down to 5kts after reaching the expected path of the convoys.
Red group routes at the start, Show All, playing Blue.


The Red subs stop navigating after just a few miles, they either stop completely or do roundabouts on the spot at 5kts speed.
Red group routes at the end of the game, 10 days gametime has passed, showing they did go nowhere.


I tripped over ZJU V3023 at the end of the game, taking a closer look, it is laying in place, going nowhere, speed at 5kts, it's course alternates between 77 and 249 degrees and sometime it also does instantaneous depth changes between deep and shallow.
It can not move, even after Show All, clearing it's path and plotting a new one, it does not obey move orders.

While laying in wait could be a good ASW tactics it's not what the AI was scripted to do here.

I only attached an end game save, the issue is very easy to reproduce, restarting the scenario playing blue, red subs behave the same way every time.

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Just checked HSD2 4.0, same symptoms.

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HDS2 5.0 too.