ESXi to Synology NAS iSCSI slowdown out of nowhere

Out of nowhere I'm experiencing incredibly slow connections between my esxi hosts and my synology NAS.  I have 3 hosts, 2 Mac Minis running in HA and a Dell Server.  My Synology NAS is on the latest firmware with 3 of the links link-aggregated.  I noticed while copying files to one of my VMs over the network (the VM had a share going over AFP) that I was getting maybe 12 MB/s.  Then I noticed some of my other systems were quite sluggish.  I tried creating a new iSCSI LUN with some drives that have not been used on the NAS.  While it did show up on my esxi hosts and I was able to format it, migrating to it has taken too long and keeps timing out.  I've tried restarting the NAS units and the hosts.  All drives in the NAS appear to be healthy.  No configuration changes have been made for at least a month or two but I did check all settings in esxi and on my network switch to no avail.

Any ideas?