Hearthstone portal apparently can spawn anywhere (Durotar, Stormwind, Valdrakken) regardless of where it last occurred, which I doubt is intended based on how portal spawning worked for the Diablo IV cross-promo. This also ties in to the issue concerning sharding where one group will say they saw it in Stormwind, while others say it never appeared for them in that location.
3/12/24 Update:
We’ll have to see if this really fixed the problems.
Hoping they fix this in the big maintenance tomorrow because it’s the same where I am - this last hour it hasn’t spawned anywhere.
I went to Stormwind twice when there was supposed to be a portal up, but there wasn’t one. First time I waited 45 minutes because people were saying it was not always on the hour, second time only 10. Hopefully the drop rates for these items aren’t extremely low considering we are missing almost two days of the event (late event start time, every time I check there are no portals, and long maintenance). Also hopeful we will get a fix or that someone will discover the expected rotation of this event.