Came across this bug though when fighting mechanoids. Every shot would only do 10 damage and through up this error log. Only combat mod im using is Yayos combat adopted. Also, not sure that mechanoids should be affected by shell shock.

Exception ticking FT_Bullet_ATShell2484420 (at (126, 0, 132)): System.InvalidOperationException: Collection was modified; enumeration operation may not execute.
at System.ThrowHelper.ThrowInvalidOperationException (System.ExceptionResource resource) [0x0000b] in <eae584ce26bc40229c1b1aa476bfa589>:0
at System.Collections.Generic.List`1+Enumerator[T].MoveNextRare () [0x00013] in <eae584ce26bc40229c1b1aa476bfa589>:0
at System.Collections.Generic.List`1+Enumerator[T].MoveNext () [0x0004a] in <eae584ce26bc40229c1b1aa476bfa589>:0
at BlackArmoury.Bullet_AlongOnWayDamage.TakeDamage (UnityEngine.Vector3 exact) [0x000cf] in <649e8ebc1f6149808454918d1b4e3066>:0
at BlackArmoury.Bullet_AlongOnWayDamage.Tick () [0x00130] in <649e8ebc1f6149808454918d1b4e3066>:0
at Verse.TickList.Tick () [0x0015c] in <00638943358e4807bd44cd7bc8f572da>:0
UnityEngine.StackTraceUtility:ExtractStackTrace ()
(wrapper dynamic-method) Verse.Log:Verse.Log.Error_Patch2 (string)
Verse.TickList:Tick ()
(wrapper dynamic-method) Verse.TickManager:Verse.TickManager.DoSingleTick_Patch5 (Verse.TickManager)
Verse.TickManager:TickManagerUpdate ()
(wrapper dynamic-method) Verse.Game:Verse.Game.UpdatePlay_Patch1 (Verse.Game)
Verse.Root_Play:Update ()

Hope this help.