Since Ubuntu works fine I would think that most hardware issues are out.
The problem appears to be an incompatibility between the driver the PC
is using and the router.
I would still try another cable as what one driver (Umbutu or Windows
based) will accept as error free another might reject due to a different
threshold settings written into the driver code.
In the past this was usually the two devices fighting for control when
both were in auto mode due to almost identical data sampling rates.
Many interface companies "fixed" this problem by doubling their devices
sample rate in the past. If the driver/device data sample rates match
or are close you may see the two devices fail to work while both try to
become the master and are switching between the multiple speeds with
neither of them waiting long enough for a match to occur.
If a cable change does nothing to help with the problem I would try to
manually lock the PC to Giga and see how the connection works. A few
tests should nail down if this makes things work for you.