Interesting...I've had similar dropout issues with google devices, in particular google homes and hub. I had this with the Orbi mesh router as well before I switched to the Deco M5. So even though...

Yes, you do, and set the deco to run in AP mode.

Whilst travelling recently the deco M5 app notified of a firmware upgrade. Because I was away on business I ignored the update,. Now back home the deco app wrongly says there is no update available...