Same here. Logged in this morning on my PC, had 3 quests (re-rolled one). Then 20 minutes later one of the quest had disappeared when I logged on my phone.
I think it was my new quest from today (not re-rolled) that disappeared.
Edit: made it clearer
Actually, after the vanished quest i didn’t get a new quest today. Probably this happened to everyone but at this point we lost 2 quests… 
Same here. Yesterday and today, the 3º quest missing. i always stay with 2 quests and wait the 3 to reroll the painful quest. 2 days in a row Blizzard ¬¬
I’ll add my name to the list. NA server.
I have had the same two quests for probably about a week before the launch of SOU.
Play 10 Demons (50 gold)
Play 6 Secrets (50 gold)
The morning of SOU launch, I got a third quest and completed it before the SOU launch quest came in. I completed the launch SOU quest within a couple hours of receiving it.
The next morning I had a third quest and completed it.
I still had the same two quests in my log last night:
Play 10 Demons
Play 6 Secrets
This morning I woke up and had no new quest for today at 5AM PT.
I was able to reroll the Secret quest into Play 30 Shaman cards and I’m in the process of completing that quest.
Can’t edit posts anymore? Just to be clear. I didn’t have a quest disappear, I just didn’t get a new one with the daily reset today.
I have the same issue as others in this thread. I have not received a new quest on the 7th or 8th despite having an open quest slot both days.
One of my quests I still had had yesterday also vanished today. Please fix this bug soon, there’s a lot of ingame gold lost to it!
Honestly, they can gift us players a triple gold reward for daily quest to compensate…
The bug is basically this and has been happening since launch of Uldum:
Any current quest you have will automatically be re-rolled by the game, you will still be granted the choice to re-roll a quest yourself, but no new quest will be granted if there is an available slot.
You’re wrong. If you have 2 empty slots - you get new quest as normal.
Doesn’t match my experience at all. I’ve seen quests disappear, not being re-rolled for me. And I got a new quest this morning although I had 2 empty quest slots.
But it is well possible that the bug causes different problems for different players. As long as Blizzard does not acknowledge the problem, we can only speculate.
I had a third quest slot open and I did not receive a new daily quest when I logged in this morning.
I had 2 quests, expansion came out and I got the legendary quest but not a new daily, which I believe is normal and to be expected, since I only had the one slot free and the legendary quest took priority. I completed the legendary quest yesterday, which left me with 2 quests again (one slot available) and today I do not have a third quest. I do not know if it disappeared or if I just didn’t receive it.
Yesterday (08/06/19) a new addition was released. There was a place for the legendary quest. After its completion, there were two daily tasks left. Everything happened before updating daily tasks. The next day, one old daily task and one new one are shown at the entrance. One old thing has disappeared. And the amount of gold also has not changed. On the second day the same thing happens. Password reset, region and language changed. Nothing helps. Solve the problem, two quests have already disappeared. What is the point of playing without gold.
I had 2 quest slots filled last night and the same 2 quests this morning. A new daily quest was not added. Americas server
Americas server; same issue as OP: My daily quest for August 7 disappeared, except in my case, the quest disappeared shortly after midnight PT.
Additionally, as many other people here are reporting, I didn’t receive a new daily quest for today, August 8, even though I had a quest slot open. I’ve exited out of and re-launched the Blizzard app, but that hasn’t fixed anything.
DETAILS
Two days ago (Aug. 6), my quest queue was full: I had 2x 50g quests (“Emerald Dream” and “Weaponmaster”) and the new “Welcome to Uldum” quest that awards 3 Uldum packs.
I completed the “Welcome to Uldum” quest that same day (Aug. 6) shortly before midnight PT and then went into my Quests to re-roll the 50g “Weapomaster” quest. It was just about midnight when I went to re-roll, and just as I re-rolled the quest (which re-rolled into “Rogue or Warrior Victory”), my new quest for yesterday (Aug. 7) popped up — “Watch and Learn.”
So at this point — just after midnight Aug. 7 — I once again had 3 quests: Still had “Emerald Dream” from before; had my new quest for Aug. 7, “Watch and Learn”; and I had “Rogue or Warrior Victory” as my re-roll of “Weaponmaster.”
After re-rolling, I exited out of Hearthstone (but not the Bizzard app). Then a few minutes later, I changed my mind and re-launched HS to see about playing a game. But when I re-launched (around 12:10a.m. PT, Aug. 7), I only had 2 quests — “Emerald Dream” and “Watch and Learn.” My re-roll, “Rogue or Warrior Victory” quest, had disappeared, even though I hadn’t played any games since I re-rolled the quest. My gold total also hadn’t changed, so it’s not like the quest was being counted as completed.
I exited out of the Blizzard app and re-launched it yesterday morning (around 9/10a.m. PT) to see if that would fix the issue, but I was still showing only 2 quests. Additionally, I didn’t have the option to re-roll either of my remaining 2 quests, meaning that the system logged my post-midnight re-roll of “Weaponmaster” as my re-roll for yesterday, Aug. 7. But the actual quest I got from that re-roll (“Rogue or Warrior” Victory") has disappeared.
Sent a message to Support about this issue yesterday and was instructed today to post here in the Bug Forum.
As of this morning, Aug. 8, I’m still showing only those 2 remaining quests — “Emerald Dream” and “Watch and Learn.” My missing quest hasn’t reappeared and I also wasn’t given a new daily quest for today (although my ability to re-roll a quest for today is active, as normal).
Blizzard has answered on reddit:
Hello, i lost 2 daily quests since the gift of 3 Uldum packs …
Should i wait for a 3rd time this night ?
I’m really disapointed with that and so sorry for you …
Big bugs eat my quests !!!
Thank you very much for the information.
I’m probably an old jerk but I think it’s a shame that they seem to ignore us here on the official bug reporting forum (I don’t know if they read, but if they do they keep silent so we have no clue) and at the same time answer relatively fast on a 3rd party forum which, in my own little fantasy world, is in no way the appropriate place to report a game bug.
Oh well, it’s probably about time that I go live in cave.
“No new quest will be granted if there is an (meaning “ONE”) available slot”
My statement had nothing to do with MULTIPLE or “2 empty slots” as you put it.
However, I acknowledge that I can only speak from my experience, and that yours may be completely different. I simply think you misunderstood what I was indicating my experience to be.