Truck Won't Reverse and Hard Disengage 4 LO

I know that 4LO can be a bear sometimes with these (mine's a 2015). I'll also admit I've let it go a while without engaging 4wd as you are supposed to do monthly.

The truck has no problem at all going into and out of 4HI. It actually goes into 4LO pretty well but then has two problems: It will not go into reverse when in 4LO. There is a loud grinding sound coming from the transfer case but it won't engage reverse. Then getting it back out of 4LO into 4H (truck is in neutral) takes a lot of back-and-forth.

I'm just about to swap the transfer case oil but also trying to plan what to do next if the problem persists.

Thank you all for the help!