Thank you. I did exactly those step prior your suggestion and downgrade; however I just did the ver. 386_49599 as you mention and Bang! all my IoT are back and fast responding! (I'm shock) now I'm 100% that the 388.xxxx have an issue or bug they haven't figure out. may be because they have focus on Wi-Fi 6 feature or improving 5g, nevertheless no doubt it's on the firmware . Not everyone use lots of device on 2.4 need it like me, but again not a lot of option when it come of IoT, except the long waiting "Matter" (Thread .. didn't make it

) , still love having lots of device in my house instead flipping switches