I had the same situation yesterday. My TA made reservation without my MP# on it. I called MP Service desk asking the agent to add my MP# to my itinerary and gave her UA’s reference #. She told me that she has no access to the itinerary and I should call reservations. I followed her advice and my MP # was added. Now I am able to see it on united.com. I made changes in my seat assignment and it was saved on united.com, but Amadeus Checkmytrip still showing the original seats.