Have you checked (or are you checking) availability via Expert Flyer? Maybe the 'auto upgrade' feature has a different trigger point than just 'upgrade availability'? Or there is a bug in the system?

I am waiting for an upgrade on a DXB/AMS leg. And to try to understand how they release these, I have set a number of alerts on EF. Apart from a few days, where the upgrades were available up to 30 days before departure, they are all released 4 days before. And there is a clear correlation with the seat map (which is not that surprising as most F travellers will book their seat at the time they book the trip).
On cue: the alert for F award availability on 31/3 has just come in!