It seems that there are many people having issues with combining seperate body and head animations to their metahumans.
I currently don’t have the floating head, but the neck is weirdly displaced.
I have tried setting blend masks on the face skeleton + BP but they have absolutelty no effect at all.
It looks like you have Head IK keyed to 1 in your face animation track. You’ll need to put the face animation on the control board, and find the face/head IK channel, delete all the keys and put value to 0.