Mimics don't spawn from any other than small chests, making the chest (including the item inside) disappear. There's also a bug where you can tell if the chest is a mimic by pinging it (mimics have the ping displayed way above them).
Released 1.4.1, which disables legacy mimics for now. Don't have time at the moment to track down the root cause, but this should prevent it from eating the items.
Mimics don't spawn from any other than small chests, making the chest (including the item inside) disappear. There's also a bug where you can tell if the chest is a mimic by pinging it (mimics have the ping displayed way above them).
A video showing both of these bugs in action.
Mods: