I did not receive items of the correct level.
First observation, my “1 dungeon” reward ilevel was lower than my “4 dungeon” ilevel.
Second observation, all my ilvl were lower than expected. I had completed at least nine 14+ dungeons and a few 11s. My ilvl were 220, 223 and 200. It should be 226, 226 and ?.
This happened on character Dagruk.
Thank you
Similarly, on my character Nosklock - Tichondrius, I completed a 16, 15, 14, and a number of other dungeons last week and my highest ilvl loot offered was 216 instead of 226.
Yes me also. Completed a +14 and only got a 210 from vault.
I am experiencing the same problem on Zul’Jin. I completed well over 10 +15 keystones last week and got 210, 216, 220 gear as rewards.
Character name:
Softkill-Zul’Jin
me too - I completed a +12 this last week and was expecting a 223 item from the vault, I’ve logged in to find a 200 headgear - help please? 
Bekkii - Aerie Peak
Can confirm my key order was 16 - 15 - 14
My 16 and 14 were 226s but my middle option, the 15, was a 210. It makes no sense!
So much for one last hurrah!
same: 15, 4 14s, 10 13-14 and rewards 213, 223, 216 on my Character Dewluthien Thunderhorn
Yeah it seems that Blizzard broke the vault for a lot of people though not all. Getting conflicting reports in the guild. For me personally it’s broken.
Thanks Blizzard!
Toon 1 - +14 (Untimed) - 210 from vault
Toon 2 - +15 (Untimed ) - 223 from vault
Toon 3 - +15 (Timed) - 226 from vault
WTF?
Same on this character, did a 14 in time and a 15 not in time, and had a 216 item in my m+ slot.
Same issue on my shaman. Should have had 2 226 items and a 220 item.
Not sure what happened with my box. I am pretty sure I did a 15 last week. Box had a 220 ilevel weapon for me and a +13 key.
same with this character, i complete a +15(untimed) and my high reward in vault is 213 . . .
Same issue 220 226 220. I have timed like 7 18s few 15s.
Same issue, reward for first dungeon is 200 ilvl (completed 15’s) and reward for 4 dungeons is 210 ilvl (lowest completed was an 11)
Same issue…
15 timed and got 210
They’re working on it: https://twitter.com/WarcraftDevs/status/1410000434798817282
Edit: And it is now resolved https://twitter.com/WarcraftDevs/status/1410258469035274242. You gotta put in a ticket if you opened the vault while the issue was occurring and don’t have the higher ilvl gear that you should.