Mostly got it working based upon Pepisolo's entry.
First, updated "fully" functional code:
<entity name="bob" category="Ship" ship_category="Wander_3x3"
display_name="Small Test Enemy"
behavior="Attacker"
speed="100"
max_health="100"
periodic_movement_mode_interval_min="0"
periodic_movement_mode_interval_max="5"
image_folder="Familiars"
image_name="Ram"
>
<hitbox radius="32" />
<periodic_movement_mode type="Reposition" related_point="10,10">
<modifier type="MovementSpeed" math="Set" magnitude="1000" />
</periodic_movement_mode>
</entity>
However, one Reposition has started, it cannot end and generates a fatal error.
FixedUpdate: System.NullReferenceException: Object reference not set to an instance of an object
at GameEntity.ClearPeriodicMovementMode () [0x00000] in <filename unknown>:0
at Flock.ReevaluateAIOrders () [0x00000] in <filename unknown>:0
at CombatEncounter.<DoCombatStep>b__16 (.Flock flock) [0x00000] in <filename unknown>:0
at CombatSide.DoForFlocks (.ProcessorDelegate Processor) [0x00000] in <filename unknown>:0
at CombatSide+<>c__DisplayClass4.<DoForFlocksThatAreHostileToMe>b__3 (.CombatSide side) [0x00000] in <filename unknown>:0
at CombatEncounter.DoForSides (.ProcessorDelegate Processor) [0x00000] in <filename unknown>:0
at CombatSide.DoForFlocksThatAreHostileToMe (.ProcessorDelegate Processor) [0x00000] in <filename unknown>:0
at CombatEncounter.DoCombatStep (Single EffectiveDeltaTime) [0x00000] in <filename unknown>:0
at World.DoWorldStepLogic (Single effectiveDeltaTime, Boolean IsFirstLoop) [0x00000] in <filename unknown>:0
at World.ProcessSimStepOnPrimaryMachineOnly (Int32 SimLoopNumber) [0x00000] in <filename unknown>:0
at Game.ProcessSimStep () [0x00000] in <filename unknown>:0
at ArcenMainCameraImplementations.MainUpdateLogic () [0x00000] in <filename unknown>:0
Stack Trace: at GameEntity.ClearPeriodicMovementMode () [0x00000] in <filename unknown>:0
at Flock.ReevaluateAIOrders () [0x00000] in <filename unknown>:0
at CombatEncounter.<DoCombatStep>b__16 (.Flock flock) [0x00000] in <filename unknown>:0
at CombatSide.DoForFlocks (.ProcessorDelegate Processor) [0x00000] in <filename unknown>:0
at CombatSide+<>c__DisplayClass4.<DoForFlocksThatAreHostileToMe>b__3 (.CombatSide side) [0x00000] in <filename unknown>:0
at CombatEncounter.DoForSides (.ProcessorDelegate Processor) [0x00000] in <filename unknown>:0
at CombatSide.DoForFlocksThatAreHostileToMe (.ProcessorDelegate Processor) [0x00000] in <filename unknown>:0
at CombatEncounter.DoCombatStep (Single EffectiveDeltaTime) [0x00000] in <filename unknown>:0
at World.DoWorldStepLogic (Single effectiveDeltaTime, Boolean IsFirstLoop) [0x00000] in <filename unknown>:0
at World.ProcessSimStepOnPrimaryMachineOnly (Int32 SimLoopNumber) [0x00000] in <filename unknown>:0
at Game.ProcessSimStep () [0x00000] in <filename unknown>:0
at ArcenMainCameraImplementations.MainUpdateLogic () [0x00000] in <filename unknown>:0
at System.Environment.get_StackTrace()
at ArcenDebugging.ArcenDebugLog(System.String Message, DebugLogDestination Destination, Boolean IncludeStackTrace, Verbosity Verbosity)
at ArcenDebugging.ArcenDebugLog(System.String Message, DebugLogDestination Destination, Verbosity Verbosity)
at ArcenDebugging.ArcenDebugLog(System.String Message, Verbosity Verbosity)
at EngineConfig.WriteToErrorFile(System.String ErrorFile, System.String ErrorName, System.String ErrorText, Boolean SuppressArcenDebugLog)
at EngineConfig.WriteToErrorFile(System.String ErrorFile, System.String ErrorName, System.String ErrorText)
at MainCameraLogic.LogWritten(System.String LogString, System.String StackTrace, LogType Type, System.Exception Cause, Boolean CameFromUnity)
at MainCameraLogic.LogWritten(System.String LogString, System.String StackTrace, LogType Type, System.Exception Cause)
at ArcenMainCameraImplementations.Log(System.String LogString, System.String StackTrace, LogType Type, System.Exception Cause)
at ArcenMainCameraImplementations.MainUpdateLogic()
at MainCameraLogic.Update()
I'm not sure if it affects only Reposition or all other Periodic Movement types. As it stands it is unuseable.