I tried downgrading the devices, but without success. I attempted it using two previous firmware versions: X20 4.0_en_1.2.0 Build 20231221 Rel. 56452_US_EU_B4_SG_up X20v4_en_1.5.5 Build 20240718 Rel....

Deco X20 system worked perfectly for 3 years. Recent firmware update has caused complete network collapse. System now generates 784 NRD errors per hour and IoT devices cannot connect. TP-Link support...