Just tested this out for myself and I get the same freaking problem. It's bad enough that they force us to use our data rather than playing from local storage, but the streaming quality is ABYSMAL compared with every other video app known to Android.
What the heck is the point of buying HD when it can't even stream SD video reliably? Piece of crap video player. This, on top of the constant nonsensical errors that require a device restart. +Google Play
should be utterly embarrassed that "Play Movies" bears the +Google
name. Then again, the Googleverse has become a desolate graveyard of useful features and basic functionality, as of late, so we really shouldn't be expecting anything but endless frustration using Google services, to say nothing of the unspeakably horrendous customer service, if it can be said to exist at all, even for their paying customers.