UPDATE (will they never end?)
The TP-Link Deco M9 Plus mesh router, two nodes, now serves eight v2s to the Wyze app smoothly and stably, both singly and in portrait and landscape groups.
Turns out the TP-Link app Optimize Network function (choosing ‘best’ 2.4 Ghz & 5 Ghz channels to avoid detected interference) was somehow borking the 5 Ghz band instead, forcing my Android 10 phone to cycle quickly between 2.4 Ghz & 5 Ghz connections (settling on 2.4) experienced as intermittent connectivity of the phone and cams, and apparently, bad or unavailable 5 Ghz wireless backhaul.
Rebooting the Deco network (both nodes) and phone sorted out the 5 Ghz bork (which would not be unborked without it) optimizing channels in the bargain.
So apparently not my cheap-ass phone’s fault after all: