Steps to reproduce:

Place a chest, with items in it, and a iron chest of some sort.
connect them with EIO conduits, or Thermal Dynamics Ducts.
Crash as soon as they try to push items in.
Crash with Thermal Dynamics
Crash with Ender IO

Crash does not occur on 835

MC: 1.12.2
Iron Chests: 7.0.51.836
Forge: 14.23.4.2756