Same stuff happened to me: here is what i know (SEND IN A TICKET!!!):
From the forums… Lethal Bug Report
"시체전문가212 posts
12h
Lethal Bug Report (All items in a shared item stash disappear)
Bug Acting Conditions
Put items in a shared item stash as a ladder extension character
Put items in a item stash as a ladder original character
When you check the shared item stash with the ladder extension character, all items evaporate"
Also check Diablo II: Resurrected Patch 2.5.2 - Release Notes (11/1) - #5 by PezRadar1