As far as I'm aware the shaft is floating inside the diff, trimming it will help with the pressure on the bearing?
I'm pretty sure the shafts are stock, the passenger side shaft is longer by 1/2 in or so than the driver side's.
The shaft is probably bottoming out on whatever the center of the diff is. Usually a cross style center pin that connects all the spiders together. Just depends on the actual construction of the locker you have.
I have a feeling if you trimmed off 1/8” or so, you’d probably be able to seat the axle fully and if not get tight.