On a flight last week, I was #1 on the waitlist for a GPU and there were three seats open within about 2 hours of take off. I was watching it like a hawk, and then saw R1. Waited a minute or two, no email about my upgrade. So I wasn't going to take any chances, phoned in. First agent said "I can't do anything, it's under airport control". HUACA. Second agent took about 30 seconds to process the upgrade.
The weird thing is, she used a "new" GPU from my account to process it, not the GPU that was waitlisted. So I had basically used 2 GPUs for the upgrade. I waited a couple of days after the flight, no redeposit of the extra GPU. Emailed 1K, and within 4 hours got a nice email with 1 GPU redeposited.
In this situation I didn't "queue-jump" because I was #1 on the list. But someone else easily could have. Just encourages me to queue-jump again in the future... very annoying...
Meanwhile as others have commented, I am noticing fewer and fewer flights with R availability at booking time... it's a bait and switch game. Many other things about United have been really improving over the past several months but this issue remains a bone in the throat...