@TP-Link thank you for your help.

@TP-Link yes, a different Deco unit lost 2.4ghz signal source at the same location. The original unit regained the 2.4ghz signal source on the new location. Distance between main deco and 2nd deco is...

@TP-Link I tried switching my 2nd and 3rd Deco, 2.4Ghz is missing as well when placed in that position. I will send the picture through email.

My 3rd Deco M5 only gets 5 GHz while signal source (2nd Deco) has both 2.4 and 5 GHz. I already reset the unit and gets both 2.4/5 GHz when near the main Deco.