PC EU, owned since 2018.
If you unlock the reward via visiting DLC zone, but then teleport somewhere else without claiming, it will be locked again and forever. 🙃
PC EU
Claimed on day 1.
Own DLC already from purchasing it and have, some time after purchasing also subscribed to ESO+.
Have purchased all other DLCs except the Scribes of Fate one which released after I subbed to ESO+
Says can't claim for 18 hours on the DLC itself and that the last day of the month reward is not going to be available as the month will reset before I can claim it.
Also, not sure whether it is relevant but I never got the usual pop-up for the daily rewards to be claimed when I logged on. And when I first tried to view the daily rewards to see how the "claim" would work for something that I already had (because I wanted to make sure it didn't show me as skipping a day, which of course is exactly what happened) it would not let me get to it from the usual menu. I could open the crown store and go to the seals of endeavour store but the other icons, including to view daily rewards, were missing. I had to try numerous times after hopping between zones before they appeared and they are missing again now after checking my DLC purchases.
ETA: Travel to the Deadlands worked for me too. Pop up for rewards when I arrived, able to "claim" and the last day now unlocked.