Satellites wont connect iPhone & Sonos to wifi after 12 hours

I have an Orbi RBE771 router with three RBE770 satellites connected via Ethernet CAT6 back-haul through two unmanaged Netgear switches. The router and one satellite are in the house, the other two satellites are in the shed.

All networking equipment, Sonos and Ring devices have fixed IP reservations.

iPhones & iPads use DHCP.

DHCP has a range of 89 IPs (.10 - .99) despite only around 10 DHCP clients having leased IP reservations.

Firmware is V10.5.20.10_2.2.51 and Wi-Fi security is WPA2-PSK + WPA3-Personal. There is no ability in the web-UI to only select WPA2.

After factory resetting the satellites, the wifi network works normally for about 12 - 24 hours. Then iPhones, iPads, and the Sonos speakers in the shed can still see the SSID but are unable to connect to Wi‑Fi. And the Sonos app does not display the lost speakers.

Ring cameras around the house and the shed remain connected and fully functional.

Rebooting a satellite does not resolve the issue; it only enters a Config Sync state and constantly flashes white. Only a factory re-set of the satellites gets it to a Good state ... but then the problem re-occurs :(

What is the most likely cause and recommended fix?