One of my armies cannot be selected or moved. Whenever I click on it, the game's UI seems to select the last army that I had selected. It says "locked by battle" as the status, but other than that it seems very confused.

I recently had a battle in this area, using this army. It broke right after that.

Save is attached: Khmer Turn 139.ctr

Diagnostic logs have a critical error, an out-of-bounds array access: "Index was outside the bounds of the array." This appears in the logs from when I made the save, as well as a few other logs (maybe when I click the unit?)

This is the stack trace of that error (file: Diagnostics (2021'06'20 @1148'39''466''')p1589.html:

Amplitude.Mercury.Simulation.ArmyActionHelper:FillAttackSettlementFailures(System.Reflection.MonoParameterInfo, System.Reflection.MonoParameterInfo, System.Reflection.MonoParameterInfo, System.Reflection.MonoParameterInfo, System.Reflection.MonoParameterInfo) Amplitude.Mercury.Simulation.ArmyActionHelper:FillAttackSettlementFailures(System.Reflection.MonoParameterInfo, System.Reflection.MonoParameterInfo, System.Reflection.MonoParameterInfo, System.Reflection.MonoParameterInfo, System.Reflection.MonoParameterInfo) Amplitude.Mercury.Simulation.ArmyActionHelper:CanExecute(System.Reflection.MonoParameterInfo, System.Reflection.MonoParameterInfo, System.Reflection.MonoParameterInfo, System.Reflection.MonoParameterInfo, System.Reflection.MonoParameterInfo, System.Reflection.MonoParameterInfo, System.Reflection.MonoParameterInfo, System.Reflection.MonoParameterInfo) Amplitude.Mercury.Simulation.ArmyActionHelper:FillArmyActionInfo(System.Reflection.MonoParameterInfo, System.Reflection.MonoParameterInfo, System.Reflection.MonoParameterInfo) Amplitude.Mercury.Interop.ArmyCursorSnapshot:Synchronize(System.Reflection.MonoParameterInfo, System.Reflection.MonoParameterInfo) Amplitude.Mercury.Interop.Snapshot`1:Synchronize(System.Reflection.MonoParameterInfo) Amplitude.Wwise.Interop.AkLogger+ErrorLoggerInteropDelegate:Invoke(System.Reflection.MonoParameterInfo) System.AsyncCallback:Invoke(System.Reflection.MonoParameterInfo) System.Threading.ExecutionContext:RunInternal(System.Reflection.MonoParameterInfo, System.Reflection.MonoParameterInfo, System.Reflection.MonoParameterInfo, System.Reflection.MonoParameterInfo) System.Threading.ExecutionContext:Run(System.Reflection.MonoParameterInfo, System.Reflection.MonoParameterInfo, System.Reflection.MonoParameterInfo) Amplitude.Wwise.Interop.AkLogger+ErrorLoggerInteropDelegate:Invoke(System.Reflection.MonoParameterInfo)

Other logs mostly have noise but there is a tantalizing warning-level log message in a few from 10 minutes before the save (so probably during the battle, but I'm not sure): "Could not retrieve defender army / district with guid 17135 for battle prediction." 

This is likely a duplicate report of this other bug report which contains an additional example in another save file, but the log extracts provided here seem quite useful. Thanks for that.