Orbi RBR50 throttling internet speed?

Having some puzzling issues that just started cropping up with my Orbi router.  

When I reset my DSL modem to factory default settings recommended by my ISP, I'm getting close to the 50 Mbps connection that I should be.  However when I bridge that modem over to the ORBI, my download speed reduces to 5-6 Mbps maximum.  
The ISP doesn't offer any support for 3rd party router connections at all.  

Setup was working fine for a year and a half, and speed was good prior to this past week so I don't know what changed suddenly, but my internet speed completely crashes whenever I connect my Orbi.  With 2 kids doing school from home plus me working it's a nightmare. 
 
Only thing that changed on my end is I added 2 newly built PCs to the Wifi network.  Note that the speed decreases even when I'm connected directly to the ISP modem, so it's hard to tell if the issue is in how I set up the bridge or if something's gone wrong with my Orbi hardware.