What's that bandwidth usage on the WAN graph? Is either the inbound or outbound traffic look to be maxing out your Comcast connection? Do you have any rate limiting set up on the WAN interface. eg.
config system interface
set inbandwidth <value>
set outbandwidth <value>
Aside from this, you may want to check for possible duplex/speed mismatch on both sides of the 30E connection. eg. WAN and LAN.
#diag hardware deviceinfo nic wan
Description Marvell NETA Gigabit Ethernet driver 00000010
If you see any Rx or Tx errors wait a couple minutes then repeat the diag commands above. If the error counters increase then you may have a duplex/speed mismatch. Do the same to the lan port side.
#diag hardware deviceinfo nic <lan |lan1|lan2|lan3|lan4>
Basic network troubleshooting applies - try to determine possible cabling issue, switch issue, comast modem issue, etc. If you can log into the comcast modem, you might have access to the logs there.
Also do not rule out a cable problem between your computer and that switch.
NSE4/FMG-VM64/FortiAnalyzer-VM/6.0 (FWF30E/FW92D/FGT200D/FGT101E/FGT81E)/ FAP220B/221C