Quick Update: There was a cover plate concealing a couple screws that made it easy to remove the lock. So now I've been able to remove the lock (and thankfully the hitch receiver) and get a better look at what is going on. There are definitely a few pins that are stuck. I've tried PB Blaster, a hammer, and even some dental tools to see if they come unstuck but no progress. However, now that I've got the unit removed I can just buy a replacement part from the hitch manufacturer.
Thanks to everyone who offered advice! Take care.
