This just happened to me today on a flight booked for ~11 days from now. I DM'd @DeltaAssist with my Diamond # and confirmation # and I saw the statuses change from "Upgrade Eligible" to "Upgrade Requested." Quick fix, but still odd.
FWIW, it's a roundtrip with 1 leg on a small aircraft with no first/biz cabin, and the other leg with a first cabin.