RBR20 slow connection to PC (Ethernet & WIFI)

Hi - struggling with the following problem:

I have gig service from Rogers, with a Hitron Coda-4582 modem/router.  I have disabled the gateway function.

Have a wired connection going from the Hirtron to the RBR20, firmware V2.3.5.30, in router mode.

Then a wired connection from the RBR20 to a d-link 8 port switch.

The PC is then wired into the d-link

All lights indicated Gig connections.   Network adapter in PC is a Realtek PCIe GBE Family Controller - it shows 1.0 Gbps under status.

Speedtest.net showing download 14-16 Mbps, upload 25-30 Mbps.  (similar speeds happens if I switch the PC to WIFI)

If I skip the d-link switch and connect the PC directly to the RBR20, same slow speeds

The kicker is - If I connect the PC directly into the Hitron modem I get 900-950 Mbps download, without changing any setting or rebooting anything.  Also - all my wireless devices are fine...my iPhone X regularly gets 350+ Mbps speeds.

Have rebooted dozens of times.  I'm convinced everything worked when I first bought the Orbi.  Noticed the slower speeds since working from home the last couple of weeks.