I recently bought a 3 set of Deco M4s and everything went well while setting up and everything After few days of working regularly, the 3rd deco which was connected wirelessly to the main deco stopped

I am using Deco M4 (2 packs). 1st main Deco is at the first floor connected wired to the modem, 2nd Deco unit is connected wired from the 1st Deco unit at the ground floor. I am experiencing intermitt