For your case, you can try to unscrew one of the LB100 and then screw it back to the lamp base, check whether the Kasa app can control this LB100 or not. If still have issue, it's suggested to turn...

On the Deco App, go to More->Wi-Fi, then you can turn on or off the 2.4G and 5G network.

If your modem or your computer do you have special function(which I can't know), in a normal case, when the USB modem plugged into the TL-MR3020, the computer can't see the USB modem directly.

Yes, if you delete the deco on your account, and then readd it with the new account, it will bind to the new account, but need reconfigure the deco units

on the management page of the TL-WR941HP, you can go to the Advanced->Adavnced settings->wifi coverage to change the coverage of the router. Here is no option to change the transmit power

How many deco do you have? Do you still have the same unstable issue? or after you change the master deco, all the deco network is working properly? How about the firmware version and hardware...