There is nothing wrong with you, but the website. There are lots of threads on this. Any F on LH on UA outside of about 1 or 2 weeks is phantom.
Just yesterday I had a call from Customer Service because I continue to complain about this for over one year. The CS agent basically told me that there was not a problem, but that others were just happening to grab the availabe seat basically in the same "mil a second" as when I hit the button. Contradicting herself she also told me that they were aware of this problem and working on it (for over 1 year?)
Basically she ended by giving me the propaganda about how great Smeisk was and how we needed to respect "Mr" Smeisk.
It is just the new UA.