Hi Xaymar,
After going through our logs it seems that motion blur is kind of unstable at the moment. There are several issues logged (most sequencer related) I found this one that seems similar: Unreal Engine Issues and Bug Tracker (UE-27455)
The dark shadow is a bug that hasn’t been addressed yet and I have logged a bug report here: Unreal Engine Issues and Bug Tracker (UE-34678)
Thank you for submitting a report!