I have possibly a similar issue. 

Privateers on a cliff besieged a town, on the following turn they are attacked by an enemy AI player if i auto it throws the following exception and combat never resolves and the turn can't be skipped. If i attempt to manuel "Ready to fight!" changes to "waiting for opponent" and it just hangs.

Hope this helps, 

I was finally going to win a hard AI game with hard world settings using Roving clans too...

NullReferenceException: Object reference not set to an instance of an object
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AILayer_UnitDesigner.AILayer_Encounter_EncounterRoundUpdate (System.Object sender, .RoundUpdateEventArgs eventArgs)
AILayer_Encounter.Encounter_RoundUpdate (System.Object sender, .RoundUpdateEventArgs eventArgs)
Encounter.OnRoundUpdate (.RoundUpdateEventArgs e)
Encounter.ForwardRoundUpdate (.RoundReport roundReport, Boolean immediateParsing) GameClient+<EncounterRoundUpdateProcessor>c__Iterator584.MoveNext () Amplitude.Coroutine.Run ()
GameClient.ProcessOrders ()
GameInterface.UpdateMessageBoxAndProcessOrders ()
GameClient.UpdateMessageBoxAndProcessOrders ()
Session.Update ()
Amplitude.Unity.Session.SessionManager.LateUpdate ()

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V1.4.4 S3  (64-bit)

Could you upload the save game somewhere and provide a link to the file ?

It would be helpful for the devs to be able to have a look ...