UPDATE:

I contacted the ambassador service, who within 45 minutes responded that the property could not see the $43 room charge (which was clearly visible at the top of the invoice they sent), but that she could (my anytime ambassador) and would refund it. She further explained that I was correct about the missing F&B credit, and that the property had decided to refund me the entire $29.

So all's well on the billing side, but the frequency with which this happens is annoying, and without the Ambassador service, I would have let it go. It just takes to long to interact with the accounting side of the house for almost any property. (I used to suspect this is the reason these billing snafus keep happening, since who has time to pursue a $10 refund for hours? It is odd, however, as what is the incentive for an employee to do this? I doubt they have an economic benefit from it, and Marriott would be skewered once somebody found out they are training their employees to commit fraud. 🤷‍♂️)

Massive thanks to the Ambassador service!