I reckon what happened with that hoss is that

... the director/creative team of the fifth episode thought of a great idea to make the horse Significant in some way (Bran warging it, etc), perhaps going back to the books for a reference (the pale girl dying horse thing), but then the director/creative team of the sixth episode was a bit less invested in that as a plot point (because Arya ex machina just gets you out of any hole, explanation free) and whatever got filmed as the resolution never got prioritised for post-production, and got cut.

Posted By: Arizona Bay, May 24, 21:37:08