That might be just a bit too much play in the rear end. Talking with my gear installer after the fact he mentioned maybe 1-2 degrees of play in the rear. With that amount of play you very well could have the pinion getting separation from the ring. Check for any play in the pinion, in/out of the diff. Maybe a loose nut or bad bearings? I would also check the U-joints. The video doesn't show it well enough to rule them out. Drop the drive shaft and start isolating potential sources.
The front shaft does tend to have more play 5-10 degrees. Just the stack up of all the equipment tolerances (Stub-to-Hub, Stub Joint, R&P). The only play in the rear should be coming from the R&P.