My 3G USB modem (Huaway E160) was disconnected 3-4 times a day. Log entry:
"port 1 disabled by hub (EMI?), re-enabling..."

Identical problem was described here:
https://forum.openwrt.org/viewtopic.php?id=29963

I've also tried unpowered USB hub, and problem has gone. It seems that internal hub is not able to cope with power glitches (?) in 5V rail. Maybe someone will advice how to solve this problem by software? In any case this external hub 'solution' might help someone with power hungry devices connected to carambola.

jedas