This article explains the troubleshooting steps for dropped connections due to "Descheduling queue is full" as a drop code.
The SonicWall scans traffic through its DPI engine and once it decides what to do with the traffic it places them in a descheduling queue (if this queue value is set) before performing the actions on the traffic. This value was created so the descheduled packets from one flow did not impact other flows. Once the queue is full the firewall drops the packets.
Navigate to the diag.html page of the firewall by logging into the firewall and replacing main.html in the URL with diag.html.
Change the "Deschedule Packet Count" value to a larger value, for example 256.