Orbi disconnects from internet intermittently

I am having a similar problem where on two different desktops, I lose wifi, yet on iphone and ipad, wifi works fine.  windows troubleshooter says i do not have have a valid IP adress.  After a bit the wifi comes back on.

I am not sure my setup is correct.  I am using an Arris surfboard cable modem (SB190) with ethernet cable running to "internet" port on the Orbi router.  I have an ethernet cable running to a desktop computer from the orbi router "internet" port. This desktop has great signal from the orbi.

  I need to insert a switch to run an ethernet cable to an Arlo device. I tried placing the switch between the modem and the orbi but it did not seem to work correctly.  Came anyone advise me where I should put the switch in my setup.

thanks, thecos77