XUV550 Front differential

Been having an issue while in 4wd when I get the gator in some heavy snow or even some mud that puts a load on the front wheels so they have to pull they will stop spinning. I started watching the front drive shaft and its spinning where it goes into the front diff. so the transfer case is locked in like it should. Then the front end pops/grabs and the front wheels start turning. I am going to make sure the driveshaft was tight on the shaft but I am worried it is internal to the differential.

ANY ideas or anyone heard of this problem.

Thanks