Hi all, I just started playing D2R couples of week ago. having a lot of fun! that game is bringing me back a lot of good memories. Little by little i started to collect some end-game gear: goods uniques, some high runes (crafted my first enigma a few days ago 
what a blast!).
Yesterday I looted a Lo rune, feel so happy! TP back to town in order to craft a new armor for my merc (Fortitude armor) equip it on my merc and check his new stats/DPS, jeez that was a nice upgrade! before testing it I decided to sort my items a little so I log out to access my mules. I logged back in on my main char a few minutes after to test out my new mercā¦butā¦my new crafted armor was gone from my nerc he was half nakedā¦wth. I havenāt been able to try it out XDDDD.
That bug seems to be related to the old save file system which have limited size file. The bug seems to be occuring since Day1 of release and havenāt been fix yet??? srlsly? In game like D2 how could this be possible? when uāre playing on-line stuck in P1 +/- SSF getting those high runes is a real struggle.
Does Blizzard really donāt care anymore about his player base? I feel so sad about thisā¦rly. (sry for my poor english, not my native so plz donāt be mad).
Yes, there is a lot of speculation towards the issue being due to an 8 kilobyte (8192 bytes) size limit on the character file. Itās very likely some sort of hard coded file save check mechanism of some kind that theyād have to dig in deep to alter.
The first 765 bytes contains information for what class, level, quest progression, skill distribution, stat distribution, what mercenary you have and their stats, and some other things. Byte 766 and on is reserved for all items on your character, in your inventory, personal stash, the items on your mercenary, items in your cube and what item your iron golem is made from.
What happens is when you have items that would result in exceeding the 8192 byte value on save, the save file gets truncated back to 8192 bytes, meaning any newer items that exceed the 8192 byte value are cut and discarded, which results in the item(s) disappearing.
The best practice right now to avoid this issue is to avoid saving large numbers of 1x1 magic, rare, set, crafted and unique items like rings, amulets and jewels on the characters private stash and the personal inventory.
Note: The shared stash is a separate save file. I havenāt heard about any items disappearing from it.
Yes, what TDJ said is whatās most likely happened to you. They need to hurry up and fix this bug, people shouldnāt have to worry about their items poofing due to a save size limit.
Looking back at original D2 apparently itās fairly āeasyā to increase the size limit since modders were able to do it with a small amount of hardcoding, Iām sure the D2R team could do it even easier since they have the source code. 
Fixing this bug just requires them to change the file size which takes two seconds. people have been begging them to fix this for over a year, but they donāt bother to read the bugs forum, or any forum other than reddit.
When they posted a patch update I posted the first reply which was 1 minute after they posted, and I reminded them of the bug but they never went back to the topic to read it again.
Blizzard doesnāt care about us. They will never fix anything and instead will continue adding random crap nobody asked for
It happened to me too, I lost Enigma and Fortitude and Infinity, please refund me Blizz!
Thks very interesting informations, indeed my main char have his personnal stash full of rare amulets & rings.
As stated above the fix seems to be pretty easy as long as u have the source code!!! Rumors are talking about the fact it has been lost and may be they just layering stuff over it ><.
Anyway the lack of communication and warning about this is very disappointing, they donāt show any respect to us as gamer point of view.
Very sorry for your lost man 
Well so I guess thatās how my D2 returnal will end with a bitter taste. Farewell nephalems & take care 
How is this not fixed yet?
Ohh my
Yah in a couple of weeks you farmed Enigma and Fortitude.
You are one lucky guy 
Nah we first need ploot and /pX + more power to farm faster to have our items vanish more quickly. 
Wellā¦Iāve to admit that iām weak & reDwnld the game few days after saying farewell and uninstall D2R XD. Anyway I just found a Lo rune again!! and craft a new fortitude for my merc 
. Iām not gonna lie my hands are going to shake when I will have to deco tonight ^^. I really want to thanks Blizz team on this issue, thks for your support & feedback and hope the strong link you create with us over those years will never break.
This really needs to be fixed in the next patch