Today I built my own Tier 7 Energy Core on our FTB Infinity Evolved Server (2.3.5) and placed a tesseract under one of the Energy Pylons and "accidentally" configured an already used frequency from another Tier 4 Energy Core meaning that the Energy from the T4 instantly flow to my new T7.

I thought OK just change the Send/Receive directions to put the Energy back to the T4 but ... both are empty now (lost 9B RF).

The Energy Cores are about 12 chunks apart.

NO, there is no other thing on the tesseract's frequency!

Server restart fixed it.

Well thats good to hear. I wasn't looking forward to debugging that one. But my initial guess was some sort of chunk loading error.