SNR is Signal to Noise Ratio on wifi communications. Sometimes you have great signal but some noise and speed drop. Get on APP/Software to see how your SNR from Deco 1 on place of Deco 2. If below of...

Place second node on second room not on third room. Remember you need around 30/35dbm SNR between both decos to avoid performance drop.

yes, but you don't have MESH on A10. ou need amendment 802.11/k/v/r to mesh work correct. One option, A10 wifi network to cover one side and mesh of deco cover the other spots. Without K/V/R you dont...

Turn OFF wifi o A10 and use only Deco. I use in same way here: Archer C7 and 4 Decos

Maybe your dns resolver not working correct. Try change to: 8.8.8.8 / 8.8.4.4 or 1.1.1.1 / 1.0.0.1 on DNS servers.

host address wrong. tplinkddns.com not tplinkdns.com missing one D and don't forget -p27345