So far : based from observation
1. Bad inventory data is usually happened with 1 object
2. It usually happened when "ppl pick up something, not showing in inventory" -> save & exit -> data corrupted
3. Some people have this issues multiple times while on single player (im assuming not on tcp/ip games)
4. Problem happen randomly, mostly with / not by shared stash.
I think, moving forward ppl need to do some sort of questionaires like this maybe:
1. What class?
2. What level?
3. Which location you last played? (act xx town, dungeon, map etc)
4. Do you remember what last item your interact with or your last action?
5. Which file was corrupted (shared stash, specific character)
6. Which OS do you play with (xp, win 8, win10 etc)
8. Did you fresh install the game or update a game via launcher from previous sigma installation?
9. Do you have any crash while playing d2?
To prevent major drawback for the future, i can only give couple of suggestion
1. Backup your savefile (from launcher -> setting -> open application data -> backup all files in save folder) periodically
2. If you noticed a weird glitch in game item disappear, IMMEDIATELY open task manager (ctrl + shift + escape), terminate d2.exe
3. Perhaps we can create a script or an app that backup save folder (i think launcher shouldve done for us..) that stored multiple backup copies
(It is abuse-able i know, but better than losing all items / progress)
4. Play SP and not on TCP/IP if you help with it (since now we have shared stash, you no longer need mule for SP)
I already take precaution by storing my savefile once a while
Lets hope there will be something like offline tools that can "uncorrupted" your files in the future, so dont delete your characters.