If it is MTU related, then dropping your LAN MTU down may help. I've no idea what might be an appropriate value but 1400 may be a good starting point and then dropping it down another 50 each time you get the issue.
If you were so inclined, you might even use a packet sniffer to see if you're retransmitting lots of stuff to try and figure out the optimium MTU. I would expect it to be temporary, though, at least until someone figures out which bits of the network they broke and sorts it out.
Might also be something entirely unrelated!