I get the following two errors repeatedly. The workaround is saving and reloading:

Entry 1 (Warning):
Trying to save reference to a discarded thing Bauer with saveDestroyedThings=true. This means that it's not deep-saved anywhere and is no longer managed by anything in the code, so saving its reference will always fail. , label=pawn
Verse.Log:Warning(String, Boolean)
Verse.Scribe_References:CheckSaveReferenceToDestroyedThing(Thing, String, Boolean)
Verse.Scribe_References:Look(Pawn&, String, Boolean)
RimWorld.Reward_Pawn:ExposeData()
Verse.Scribe_Deep:Look(Reward&, Boolean, String, Object[])
Verse.Scribe_Collections:Look(List`1&, Boolean, String, LookMode, Object[])
Verse.Scribe_Collections:Look(List`1&, String, LookMode, Object[])
RimWorld.Choice:ExposeData()
Verse.Scribe_Deep:Look(Choice&, Boolean, String, Object[])
Verse.Scribe_Collections:Look(List`1&, Boolean, String, LookMode, Object[])
Verse.Scribe_Collections:Look(List`1&, String, LookMode, Object[])
RimWorld.QuestPart_Choice:ExposeData()
Verse.Scribe_Deep:Look(QuestPart&, Boolean, String, Object[])
Verse.Scribe_Collections:Look(List`1&, Boolean, String, LookMode, Object[])
Verse.Scribe_Collections:Look(List`1&, String, LookMode, Object[])
RimWorld.Quest:ExposeData()
Verse.Scribe_Deep:Look(Quest&, Boolean, String, Object[])
Verse.Scribe_Collections:Look(List`1&, Boolean, String, LookMode, Object[])
Verse.Scribe_Collections:Look(List`1&, String, LookMode, Object[])
RimWorld.QuestManager:ExposeData()
Verse.Scribe_Deep:Look(QuestManager&, Boolean, String, Object[])
Verse.Scribe_Deep:Look(QuestManager&, String, Object[])
Verse.Game:ExposeSmallComponents()
Verse.Game:ExposeData()
Verse.Scribe_Deep:Look(Game&, Boolean, String, Object[])
Verse.Scribe_Deep:Look(Game&, String, Object[])
Verse.<>c:<SaveGame>b__13_0()
Verse.SafeSaver:DoSave(String, String, Action)
Verse.SafeSaver:Save(String, String, Action, Boolean)
Verse.GameDataSaveLoader:SaveGame(String)
RimWorld.<>c__DisplayClass3_0:<DoFileInteraction>b__0()
Verse.LongEventHandler:UpdateCurrentSynchronousEvent(Boolean&)
Verse.LongEventHandler:LongEventsUpdate(Boolean&)
Verse.Root:Verse.Root.Update_Patch1(Root)
Verse.Root_Play:Update()

Entry 2 (Error):
System.NullReferenceException: Object reference not set to an instance of an object
at Verse.GridsUtility.GetThingList (Verse.IntVec3 c, Verse.Map map) [0x00000] in <c36f9493c9844ddaa7fb5c788416098f>:0
at Replace_Stuff.NewThing.NewThingReplacement.IsNewThingReplacement (Verse.ThingDef newDef, Verse.IntVec3 pos, Verse.Rot4 rotation, Verse.Map map, Verse.Thing& oldThing) [0x0001f] in <dd5f6b372d7741358d6491f16fb78d1f>:0
at Replace_Stuff.NewThing.TransferSettings.Prefix (Verse.Thing newThing, Verse.IntVec3 loc, Verse.Map map, Verse.Rot4 rot, System.Boolean respawningAfterLoad, Verse.Thing& __state) [0x00009] in <dd5f6b372d7741358d6491f16fb78d1f>:0
at (wrapper dynamic-method) Verse.GenSpawn.Verse.GenSpawn.Spawn_Patch2(Verse.Thing,Verse.IntVec3,Verse.Map,Verse.Rot4,Verse.WipeMode,bool)
at Verse.GenSpawn.Spawn (Verse.Thing newThing, Verse.IntVec3 loc, Verse.Map map, Verse.WipeMode wipeMode) [0x00008] in <c36f9493c9844ddaa7fb5c788416098f>:0
at Immortals.Immortal_Component.RezPawn (Verse.Pawn pawn) [0x00155] in <726cd2a0fbd540aca7aad4f0a3efa489>:0
at Immortals.Immortal_Component.GameComponentUpdate () [0x0011a] in <726cd2a0fbd540aca7aad4f0a3efa489>:0
at Verse.GameComponentUtility.GameComponentUpdate () [0x00017] in <c36f9493c9844ddaa7fb5c788416098f>:0
Verse.Log:Verse.Log.Error_Patch2(String, Boolean)
Verse.GameComponentUtility:GameComponentUpdate()
Verse.Game:UpdatePlay()
Verse.Root_Play:Update()