I have recently changed my home router from C20i to AX55.  All devices work fine except my 7-year old Samsung Smart TV. 

Basically, it sometimes cannot connect to router/internet after powering on.  I have to switch off the power supply of the TV and power on again, then it works fine.  But next time when I switch on the TV, it would either re-establish the connection with the router, or not; it just happens randomly.  But there is no such problem with the old Archer C20i!

I tried to set exactly the same settings in AX55 as in C20i, even tried guest network, 2.4GHz only, etc., etc., nearly every combination but it does not solve the problem.

The strangest thing is that if I connect C20i via LAN cable to AX55 and set it in AP mode with a different SSID, and set TV connect to it, then it will become stable (i.e. no disconnection again). 

I have searched the forum and the internet and could see a lot of issues with Samsung TV itself, but also with TP Link newer routers.  Please could you advise the solution, as it is very stupid to connect 2 routers this way.