Bought the 3 pack Deco M5.

I have one issue with one satellite deco.. it has low signal range base from application. I tried hardware reset and still low signal range, the Deco satellite (office) could not connect or is having red blinking light even if it is just outside the room. The main deco (bedroom) is okay, and the 2nd satellite (hallway) is working as expected.

Tried troubleshooting the issue, I removed the network and set the office deco m5 as the 'main' deco... however, after setting him up, the signal to hallway and bedroom is low.

Seems that there is an issue with the 3rd deco m5.. is there a way to fix this?

PS: when the office deco m5 was setup as main deco - even in LAN, my desktop is getting only 90-100mbps internet connection. if I  setup the other two as main (bedroom and hallway - both can get 200mbps easily).

I already tried changing/disabling 2.4/5 ghz but still no avail, the last deco still has issues. Even tried wifi router or AP mode. picture below shows signal strength between decos, but they are just beside each other.