I am also having this issue.

https://gist.github.com/HugsLibRecordKeeper/98ad81e7a26d228b836ef6824f4a413c

Either of you by chance test the Fishing outpost with less than 200 other mods?

Suggest you disable any other mods that effect fishing like the treasures addon and test.

I started a new game with basically the same mods. It was all fish this time. It did spawn the below fish with a -3 value.

Couldn't add thing VCEF_HabdakLongfin785772 to spawned things.
UnityEngine.StackTraceUtility:ExtractStackTrace ()
Verse.Log:Error (string)
(wrapper dynamic-method) Verse.Thing:Verse.Thing.SpawnSetup_Patch3 (Verse.Thing,Verse.Map,bool)
(wrapper dynamic-method) Verse.ThingWithComps:Verse.ThingWithComps.SpawnSetup_Patch3 (Verse.ThingWithComps,Verse.Map,bool)
(wrapper dynamic-method) Verse.GenSpawn:Verse.GenSpawn.Spawn_Patch3 (Verse.Thing,Verse.IntVec3,Verse.Map,Verse.Rot4,Verse.WipeMode,bool)
Verse.GenPlace:SplitAndSpawnOneStackOnCell (Verse.Thing,Verse.IntVec3,Verse.Rot4,Verse.Map,Verse.Thing&,System.Action`2<Verse.Thing, int>)
Verse.GenPlace:TryPlaceDirect (Verse.Thing,Verse.IntVec3,Verse.Rot4,Verse.Map,Verse.Thing&,System.Action`2<Verse.Thing, int>)
Verse.GenPlace:TryPlaceThing (Verse.Thing,Verse.IntVec3,Verse.Map,Verse.ThingPlaceMode,Verse.Thing&,System.Action`2<Verse.Thing, int>,System.Predicate`1<Verse.IntVec3>,Verse.Rot4)
Verse.GenPlace:TryPlaceThing (Verse.Thing,Verse.IntVec3,Verse.Map,Verse.ThingPlaceMode,System.Action`2<Verse.Thing, int>,System.Predicate`1<Verse.IntVec3>,Verse.Rot4)
Outposts.Outpost:Deliver (System.Collections.Generic.IEnumerable`1<Verse.Thing>)
Outposts.Outpost:Produce ()
Outposts.Outpost:Tick ()
RimWorld.Planet.WorldObjectsHolder:WorldObjectsHolderTick ()
RimWorld.Planet.World:WorldTick ()
(wrapper dynamic-method) Verse.TickManager:Verse.TickManager.DoSingleTick_Patch4 (Verse.TickManager)
Verse.TickManager:TickManagerUpdate ()
(wrapper dynamic-method) Verse.Game:Verse.Game.UpdatePlay_Patch3 (Verse.Game)
(wrapper dynamic-method) Verse.Root_Play:Verse.Root_Play.Update_Patch1 (Verse.Root_Play)

I tried it with a few combinations of the fishing mod, but the above fish always spawned with an error. It also has an item durability of an absurdly huge negative value /60.

Now I have had several deliveries. They have been all fish and all positive values. Unless the value has increased resulting in nothing being negative I am not sure why it simply started working. The only difference is now the VE fishing add ons are at the bottom and therefore loaded after the outpost mod. Though that dosen't exactly explain why it was negative for a bit.