I have read this thread and its predecessors for years. Based on the data points (DP) presented, I would estimate there is a 95% chance of the AmEx credit posting correctly if TravelBank funds are purchased immediately after selecting UA as one's airline with AmEx -- or even shortly before selection

-- as opposed to a 99.9% likelihood if waiting 24 hours.
Each of us have our own personal levels of risk tolerance, as well as individual time sensitivity in buying a ticket with those TravelBank funds.