@IgorFkx
Roaming works just fine with my Deco M9 and M5 mesh. I can have Android 9 smartphone or Surface Pro tablet connected to Satellite Deco M5, make device stream YouTube video in 4K, walk through two floors which will force mobile device roam through Main Deco M9 and Satellite Deco M9, and video will not be interrupted while I walk.
You have fast roaming and beanforming enabled in Deco app, right?
You have "mesh" enabled for your smartphone in Deco app, is this correct?
What is firmware version of your M9s and M5s?
What is brand, model and Android version of your smartphone?
Also, it may be that there is a spot between rooms were WiFi signal from all Deco units is too weak or non existent, and there device just drops connection because it has nowhere to roam. If connection drops in about the same place every time, have WiFi analyzer app installed on your smartphone and check quality of WiFi signals from all Deco nodes in that spot.