Marketing has clamped down on the e+ advance seating priviledge extended to UA elite. The logic is to keep these more valuable seats open for revenue sales so pax who buy fuller fare can take advantage of that benefit. I don't disagree with the logic even though it has affected me disproportionately as I am lately bringing 3 family companions with me. I want to see UA thrive.
So we're now limited to 1 guest per elite and must be adjacent seating. You would need to be on the same pnr for this to happen, but there is no reason I could see why they couldn't assign your associate the c seat and block the middle seat unless that seat is already taken.
This seems a strident policy change as even the most helpful angels have not been able to bust around it.