[RAY TRACING] - Ghosting shadow trail with temporal samples?

Hello all,

I am testing out the Movie Render Queue and the RT technology of UE4.
I put together a sample scene where I got a ball moving from one side of the screen to the other. I disabled motion blur and I have 8 Spatial samples with 1 Temporal sample. TAA is disabled, but I keep getting a shadow error that I cannot figure out how to trouble shoot.
Do you guys know where does the trail in the gif below come from? I am by no means an expert, in fact I am fairly novice with UE4 RT capabilities. It looks to me like the temporal samples are leaving behind residual shadows, but I cannot pin point how to debug it or how to fix it.
Any help regardding this topic will be much appreciated.

Thanks in advance,