If Energy Drain from CorpseComplex is > 0.0 and enabled,
and if a player dies with a "The Ender" from EnderIO in their inventory that has been upgraded to have energy
then the server hangs, stopping players from interacting with anything until the server has been rebooted.

The issue works in both server and sp environments.
You can grab an upgraded version of "The Ender" easily from JEI (it has a purple bar).
Could be an issue with EnderIO's uI (micro-infinity) energy system implementation, or how corpse complex interacts with that system.
Durability loss is okay, energy drain is not.
This issue does not produce a crash log, nor does it produce entries in minecraft or server logs; the server simply stops responding.