I fought tormented varshan and dropped a 2GA mythic chest. Picked it up with the rest of the loot, checked my bag and it’s not there.
Checked my stash, not there.
Ported to town and back to no avail.
Sad since I have been trying to craft one with a greater with no luck and have tried 10+ times. 
Think i saw the exact same issue against Zir last night on my Seasonal Sorc.
I have started gringin Tormented Bosses and cam across a few issues I wanted t check if they were known.
I saw a Selig Amulate drop on Tormented Zir and had a full stash, so I TP town and sell my loot, then check my chest, the mythic was not in there so I extracted the loot from the chest and sold what did transfer, then went back to Zir. Only to discover a handful of Legendaries left on the ground and no Purple Mythic.
Not sure what is causing this, TP in and out or the stash system trying to grab high priority loot, but this could be a complete killer if the mythic was GA or on your need list.
Also i seek to be seeins only 1 blue Duriel or Andariel summoning material from Tormented bosses.
Same happened to me few minutes ago … Beast of Ice dropped me Doombringer and its disappeared…
Same occurs with me minutes Ago in a Tormented Zyr, i’ve Lost a Doombringer, The item disappeared from The ground and not in chest. 
Im play in Xbox
I have had Mythics drop on ground then vanish during the loot explosion from Tormented Boss.
Figure no one will believe or care, just happen to see your post.
Hello,
Last night I did some tormented varshan runs in seasonal realm with a few friends and on the last one where I started event with my mats Tyreals might finally dropped. First uber of the season, yay! Picked it up and all other items. Marked most of them as salvage but found a few i wanted to keep, including the tyreals might of course. Then ported to town. During loading screen i was taken into character selection screen and could not enter game.
Restarted the game and was hit with a small patch of 200mb then the new patch of 3gb.
As I entered the game all the drops from the last run was gone and inventory only full of the few pieces i had since before that run. But my mats were consumed/gone from the run. I did not get the mucus eggs or the drops.
Tried relogging, but to no avail.
The strange part is that i was in discord with the friends while this happened and that call was all good and well with no connection drops.
Guess it had something to do with the patch and the servers?
Feels bad too loose out on the first uber drop and chances of getting tyreals again are slim to none… really dont wanna grind out 4 extra sparks to get it as it actually dropped…
Otherwise thank you for a great game overall, its one of the most fun ive since diablo 2!
Same happened to me. Dropped Andariels Visage from Zir. Ported to town. Logged out. Logged in, update running but pressed play. Town to legion, crash during ride. Reload. 2 or 3 items gone, along with Andariel’s Visage. This happened about 3 hours ago.
Same just happened to me. Dropped 2 star Harlequin, picked up inspected. Linked in party chat and bam game crashes, Cant log in and when i eventually did all inventory items including Mythic GONEEEEE
A friend and i both lost a mythic in a mess of items. Stash recovery stopped working as well. Fighting duriel, teleported to town, disappeared and not in stash
Hmm… Duriel seemed to drop 2 mythic items on same kill, glaive and helm. Clicked on them both (glaive then helm) to pick them up, but the helm wasn’t added to inventory after picking it up. So it vanished to thin air, and the characters inventory had plenty of space.
crafted mythic and saw the rolls + 2 GA stars and then game crashed
when I got back in didnt have the runes or materials and didnt have the item
grinded 12 hours for shroud of death crafting just for this
Just had an issue with this. I was opening caches on my Necro alt and a 2H mythic dropped. I was circling around collecting, my inventory filled up and it flipped when trying to pick it up and blinked out of existence. I already have one but the spark would have been nice.
I saw one as well but it was gone when I went to pick it up. Also mucus slick eggs were disappearing