I would look to see what system updates your operations staff did. Try rolling back the updates one at a time.
Also with SEP, make sure that the network threat protection is turned off or it will try to examine all packets coming and going which will definitely cause problems with your images and bandwidth.
Also check with your networking group to see that they have not made any changes to your networking environment (i.e. bandwidth throttling on switches or routers, subnet or VLAN changes, etc.).