Yeah, sounds like the WDT or CPLD. Make sure you have all firmwares up-to-date (can be downloaded freely from Dell's site and installed on both the Diag-OS or any other Linux OS).
WDT can be disabled from the UEFI settings, but OpnSense usually does a good job of disabling/enabling the ports. As for the interfaces: there should be 4 'standard' ports, 2 SFP and 2 Gigabit off of the SFP NIC; the extra ports on the SFP NIC need to have their speed/duplex set manually if the CPLD uses an old firmware.
By the way, it is possible the storage is next to the SoC under the heatsink.
WDT can be disabled from the UEFI settings, but OpnSense usually does a good job of disabling/enabling the ports. As for the interfaces: there should be 4 'standard' ports, 2 SFP and 2 Gigabit off of the SFP NIC; the extra ports on the SFP NIC need to have their speed/duplex set manually if the CPLD uses an old firmware.
By the way, it is possible the storage is next to the SoC under the heatsink.