So. I own little forge (1.7 latest) server with those mods:
At first server didnt have Mekanism and all its components, forestry and extra cells installed, but after updating the modpack one of my players has 1 issue: every 5 or so minutes he freezes up and has to restart minecraft. What is funny about it, is that he doesnt get any crash report or any paranormal logs. He just freezes up. Extra mods he has installed: Journey map, NEI, code chicken core. Server reports disconnect cause as disconnect.genericReason. If needed, i will edit post to contain server's logs and mod versions