For some reason Ituumak has a movement speed of 0. Buffs to his movement speed allow him to move again at the speed being added (the only one I could easily find that could effect a ranger's companion animal was the chant Blessed Was Wengridh, Quickest of His Tribe)
No clue what caused it, but some stuff that might logically relate that took place between when I last saw my good pup move and when I noticed his crippling disability:
I put the boots of speed on Sagani for a while, and then took them off.
I got revive companion and used it several times, including atleast one time where he died immediately on being revived.
I loaded my cloud save from another computer for the first time.
Kind of a bummer since I have a lot invested in Sagani, and I can't imagine she's taking it well that her hunting companion has been crippled.