However, 1000baseT devices require autonegotiation to be

"However, 1000baseT devices require autonegotiation to be active to elect the clock master (source of timing). Enabing autonegotiation on every node eases transition from 10/100Mbit/s to 1000baseT switch and LAN. There are no disadvantages of keeping autonegotiation active on all devices, because complete physical link behaviours are controlled through autonegotiation (speed, duplex, clock master and flow control). For example, to force a single speed link you can keep negotiation on, but negotiate only one speed. So the old method with autonegotiation off is deprecated everywhere, on switch and LAN cards"

" If two Gigabit devices are connected through a non-compliant Cat5 cable with four pairs, many FCS errors and retransmissions may occur. If two Gigabit devices are connected through a non-compliant Cat5 cable with two pairs only, negotiation takes place on two pairs only, so it ends up successfully choosing gigabit as the Highest Common Denominator (HCD), but the link never goes up"

" Autonegotiation is a requirement for using 1000BASE-T[4] according to the standard. At least clock source has to be negotiated, as one has to be Master and the other Slave. Several physical layer devices and drivers will allow you to force 1000 Mbit/s full duplex to eliminate autonegotiation issues"

личное мнение - проблема скорее всего в слишком большом количестве переходов, где скорее всего, что то хреново обжато, либо кабель "гниловат". Как показывает личный опыт, гигабитную сетЬ лучше делать из КАТ6 кабеля.