Updated world originally made in 21w44a to 1.18 pre-release 1.
After mining, I drop off ores in a chest and log off for the day. Log back in and ores are gone, diamonds: gone. 

inventory state, or nbt data for containers/tile entities not saving correctly for chests in worlds migrated from previous versions. Causes critical bug; item duping possible / losing items possible. 

As far as i can tell: chests placed inside villages during 21w44a world and then updated to 1.18exp1 "freeze" their contents. any updates to chest inventories are reverted upon reloading the world. Items moved from one slot to another return to the position they were in during 21w44a. Items inserted after migration get removed upon reloading the world. 

UPDATE: Restarting client is not required. saving and quitting, and reloading world still causes items to disappear (or re-arrange if items were moved from their 21w44a placement). went to an empty chest, put arrow in chest. saved&quit, and reloaded world....Arrows are gone. 

UPDATE: appears to only affect migrated worlds. Created a new world in 1.18exp1 and did not have items disappearing in chests. Reverted minecraft version to 21w44a, created new world, and ran test inside another village, putting random items in chests, then migrating world to 1.18exp1, and new items inserted into those chests would disappear upon reloading the world.