Installed 2 deco m5 units. Tried many different setups but my second deco turn red from time to time.

1.) I tried setting it up as Wifi modem - deco m5 Main - deco m5 2nd. tried it through wifi only and the unit next to each other but the 2nd units led turns red about every 10 mins. I tried wiring them together and it does register ethernet backhaul but the second unit still turns red, I tried switching the main and second unit and the second unit as a main still turns red from time to time. Is it possible the second deco is a lemon? I wanted to try it in ap mode but dunno is mesh will still work.

2.)  If my AP mode setup is MODEM - ROUTER - Deco 1 AP - Switch - Deco 2 Ap will mesh still work? I mean if say my phone is connected to main router will it automatically      transfer to the closest strongest deco as if it were on mesh? or will wifi switching from main router to deco 1 cause a dissconect?

3. If deco1 and deco 2 are in ap mode will mesh work? If im connected to deco one will I seemlessly connect to deco 2 once I get closer to it?