I think the old coupons expired on 1/31, so this would be a new batch of coupons which may now be programed not to work on Amazon.
Mine were all certs I created from points a few days prior to 1/31. They're good until 3/31/20. I think it's the system, not the certs.
I think Squidfinity is correct.
The coupons I used on 1/31 that worked for Amazon had a 3/31/20 expiration date, so I think it was an updated to POS not the actual certs.