PSA: if you had a payment error on your Postmates account when checking out and have an Amex Platinum linked to your Uber account for the $15 monthly credit, check your Uber account to see if you received the Amex credits since the payment error. The payment bug seems to punt Amex cards into an 'unverified' state which stops the Amex credits.
I didn't realize that my Amex Platinum credits not posting for two months was related to the Postmates payment bug, because Uber support was clueless as to what caused it- they just kept on repeating that my card was unverified and that's why I wasn't receiving the credit. When I pointed out that I'd used the card countless times on Uber before and never had an issue with credits posting, the agent just repeated the same drivel. Uber was able to get the card 'reverified' and credits are now posting automatically, but they refused to credit the missing months. I just noticed the connection between the two because my brother just had the same issue and the agent used the same language as the Postmates issue, and after reviewing the timing we can now pinpoint that the credits stopped the same time as the Postmated payment issue cropped up.