Just an update on my above situation.
No one can figure out what the problem is, still. UA says it's Chase's fault that the card is not linked to my MP#, Chase says it is linked. I was able to convince two of the Chase reps I talked to to call and speak directly with UA, but somehow the Chase agent gets disconnected when they try to do a 3-way between me, Chase and UA.
This has become an impossible situation. I don't even know if I'll get the 50k mile sign-up bonus either with this glitch.
One positive is that, on both outbound and return, I was able to get my bag fees waived at the counter. It's a pain, because you have to check in at the counter, track down a UA employee (most people at the counter are just baggage handlers) who then needs to get a supervisor, I have to explain the situation twice, and the supervisor does something in the system to override the fees. But at least there's a workaround now as far as bag fee waiver goes.