Currently running SF 1856 with your latest adventuremmo version; MMO-v1.6.1-1.10.2.jar.
Players when activating an ability get an inventory bug where they cannot move items around or move items inside chests.
Basically their inventories are frozen.
Messing with them and relogging losses items.
Drop spamming will replace the item stack and someone else can pickup the items.
Major dupe, have blocked using abilites so players can still level for when this is fixed.