Hello i have a lots of question please first why i cant chose WDS 5G second when i try with 2.4 ghz my internet 2.4 ghz not stable ,, every 10 sec not working ,, and for 5ghz stable settings wireless

I've faced basiccally two kind of problems. Am I received a faultly product? Sometimes in some of my connected devices showing "no internet access" but at the same time the other routers connceted wit