The most likely explanation is that you inadvertently missed a day due to the new reset times.
Are you aware that the times for the daily resets have changed recently? Now everything (daily repeatable quests, Silent NPC goodies for DB, fence/launder limits, riding lessons, daily login reward, enlightenment, etc.) gets reset at the same time, and the time is different for the NA and EU servers.
For NA servers, the daily reset is now 5 AM EST, or 6 AM EDT, which is 10:00 UTC.
For EU servers, the daily reset is now 10 PM EST, or 11 PM EDT, which is 03:00 UTC.
Which server(s) do you play on, which time zone are you in, and what time of day do you typically log into the game?
I play on PS NA and I typically login around 8-9 am ET.
I was aware of the time change but not the specifics.
I must've logged in and forgot to claim it.
When the reward turnover was 8pm ET, there were a few times when I logged off at like 7:30pm one day and logged in 8:30pm on next day. That made me miss a reward even though I logged in every calendar day. I don't think this has happened since switch to 6am ET because that is outside my normal gaming time. But depending on your schedule, logging off a little before turnover and logging on a little after next turnover, can result in missing a reward.
I know it's been said a million times, but: we should be able to skip rewards (on those days when real life takes over), without being penalised for it by having end of month rewards being made unavailable.
PC(Steam) / EU / play from Melbourne, Australia / avg ping 390