I would guess it is the Spline, like Pete said. Pull the driveshaft back and check the spline. You’ll be able to tell immediately if it’s the issue. I’m also in Rosemount, let me know if you need any help. I’ve been working on ATV’s for years.
Not sure if AC is the same as some others, but sometimes a dirty connection to the actuator will not allow the 4×4 to kick in, even if the actuator is moving. Problem i’ve had with Can-Am’s.