I don't know much about moose hunting (glitches, etc.), but I will share what I do know. Moose target another player if the originally targeted player dies or moves out of range. Is there any chance something happened with the "anchoring" player during the hunt? Keep in mind that prey animals can still harm your wolf when you're hanging off them, and bull moose can kill with just two kicks, so it wouldn't take long for the moose to switch target. (Especially if players move away after the first kick.)
I think I have heard something about moose immunity glitches on mobile, but I cannot confirm any of this. Maybe it's possible a glitch allowed the anchoring player to withstand all the attacks on some of your previous hunts, meaning the moose would not target anyone else.
Edit: I found this information in the comments of the
WolfQuest Wiki:
Moose, bull and cow can be attacked by pressing the red wolf icon that appears when you are close enough to them, but not enough to take damage. Because of this you can kill moose, and elk on your own easily.
Pretty sure this is a mobile only glitch.
I assume the moose stays targeted on that player, despite being unable to reach.