Bug Transform 'Rig' not found in HumanDescription.

I have set up a humanoid character that has a nice animation state going with walking and running. I am now trying to build on the rig I had in place but I can't add or remove anything without this error appearing.

Code (CSharp):

1. Transform 'Rig' not found in HumanDescription.

Code (CSharp):

1. InvalidOperationException: The PropertyStreamHandle cannot be resolved.
2. UnityEngine.Animations.PropertyStreamHandle.CheckIsValidAndResolve (UnityEngine.Animations.AnimationStream& stream) (at <470324f39b8e438388139f7de0e49285>:0)
3. UnityEngine.Animations.PropertyStreamHandle.GetFloat (UnityEngine.Animations.AnimationStream stream) (at <470324f39b8e438388139f7de0e49285>:0)
4. UnityEngine.Animations.Rigging.FloatProperty.Get (UnityEngine.Animations.AnimationStream stream) (at Library/PackageCache/com.unity.animation.rigging@1.2.0/Runtime/AnimationJobs/IAnimatableProperty.cs:168)
5. UnityEngine.Animations.Rigging.MultiAimConstraintJob.ProcessAnimation (UnityEngine.Animations.AnimationStream stream) (at Library/PackageCache/com.unity.animation.rigging@1.2.0/Runtime/AnimationJobs/MultiAimConstraintJob.cs:105)
6. UnityEngine.Animations.ProcessAnimationJobStruct`1[T].Execute (T& data, System.IntPtr animationStreamPtr, System.IntPtr methodIndex, Unity.Jobs.LowLevel.Unsafe.JobRanges& ranges, System.Int32 jobIndex) (at <470324f39b8e438388139f7de0e49285>:0)
7.  

I'm stuck unable to continue with my rig until this is fixed. If I ctrl + Z everything I can get it to work again.
It's stuck in a place where it works if I don't touch anything.

 

in hierarchy rename Rig to rig it will work kind of stupid but it does

 

Don't know why, but this worked, thanks!