This issue is becoming increasingly common. Every week or two, all UPS options disappear from Amazon Buy Shipping—both under my carrier account and Amazon’s. However, my UPS account works fine on Easyship and UPS.com, so this is clearly an Amazon issue.
I use SSA, so manually calculating delivery times and selecting shipping options for numerous orders is not only frustrating—it’s threatening my ability to continue selling on Amazon as it takes so much time and any errors could affect my OTDR.
Seller Support has been useless, suggesting that the reason I wasn't seeing UPS rates was because they wouldn't be delivered on time. But as anyone outside of Seller Support knows, Amazon no longer filters out shipping options based on delivery promises--that flawed policy only caused more errors, and removing valid shipping options only ever made the problem worse.
I created another case to document the issue (17500407461), but at this point I am starting to lose hope that it will ever be truly resolved.