It looks that this issue may not be only due to the Linksys firmware but mostly related on an Android security fix that Google rolled out on Dec 5th.

One of the phones that I have kept off the network I just tried adding it to a network on a different router Negear R6300V2 and that resulted on the wifi network on that router to go down.

BTW, the phone was not running Oreo but even after updating to Oreo the issue did not resolve so I think it is the Dec 5th security fix by Google.

Not sure if this helps the Linksys support folks.

I have not seen any updates from them for some time now.