according to reddit users... everything comes down to "loop connection" that trigger STP, hence halt/disable the port, the culprit cause by the deco system doing some "wireless mesh connection"...

Found the problem https://www.reddit.com/r/TpLink/comments/14o0osg/deco_ethernet_backhaul_megathread/ and oh yes.... both switches we use are from D-link https://www.tp-link.com/us/support/faq/1794/

hi i just install deco network consist of: 1x DecoX10 (hw v.1 / fr v.1.2.1) as pppoe modem (main unit) 4x DecoX10 (hw v.1 / fr v.1.2.1) as access point 3x DecoM5 (hw v.3.2 / fr v.1.8.5 as access...