Well, I found out what was wrong with my mortising set up – the drill bit inside the mortise chisel was bent and causing the chisel to jam. I tried another chisel that had never been used and it worked, so I went old-school. I started and ended the mortising with those whatchamacallits, chisels! Thats it!
I marked out the mortises with a pencil, then went around the perimeter with a chisel. I only went deep enough to cut the surface fibers, maybe 1/16”+, and got a nice outline. Then I inserted the next smaller chisel into my mortise attachment in the drill press and used it to remove the majority of the material. After that I just cleaned up with the chisels and it came out fine.