RBR850 providing 900+Mbps ethernet but only 25Mbps wifi to various devices...very slow wifi!

You pose an interesting question, but it is difficult to see the relevance of the cable modem given that the ORBI unit and all devices attached with a wired connection enjoy a blazing fast speed which never changed throughout this entire process.

The only slowdown was the wifi connections, and it was all of them not just some. But, lo and behold, without any further changes, updates, adjustments, or tweaks that I am aware of the situation resolved itself (within a day) and now the phones and Ipads ALL get over 800Mbps download speeds. The substantive steps I took were to save the config file (primarily so I would not have to re-enter several dozen reserved IP addresses), unplug the single satellite, select 'reset to factory' from the web page under the Advanced settings. After the main unit booted back up and appeared stable, I unplugged the cable modem for 30 seconds before rebooting it. That part was requested by the restoral process, by the way. It then asked if I wanted to restore a saved configuration or set it up afresh, so I restored using the save config file. This process enabled the refreshed Orbi to get an internet connection and provide one to wired devices. I also reconnected the satellite, but did not reset that to factory specs (and it properly reconnected to the main Orbi with no involvement on my end). I checked and at that point both the main unit and the wired desktop computer reporting full speed again, but the wifi connections were still slow inititally. This remained the case for a couple of hours, but later that same day out of curiosity I tested again and voila! suddenly my phone was blazing fast again too. Wish I could tell you for sure what happened, but I can't actually say what part of that worked or why it did not work right away for the wifi piece, but only kicked in a couple of hours later?!? I do know that I was happy to have used the save config file since it does not appear to have had any deleterious effects and saved me quite a bit of time not having to reconfigure all that stuff from scratch manually!!! The cautionary note I have seen before is not to use a saved config from a prior firmware version, but this one was fresh using the exact same latest firmware version I was going to restore back to...