cranky enet connection upon boot

My deskside machine has wired ethernet to my router. It has
forever been the case that Windows latches onto the network at
boot every time with no problems until now. I cannot think of
anything I have changed. Perhaps this is the result of an
update, but now when I boot the machine the network connection
does not take place and I have to fiddle with disabling/enabling
the adapter a few times before it does connect. That's not a big
problem, but I'm curious what might cause it. ...and it is not
quite consistent - about one time in five it connects instantly
just like it used to. Hardware diagnostics don't show anything.