see if the router needs a firmware update, try changing the login credentials for the wifi (and make sure that you're using a WPA2 AES password), and if all that fails, it might be time for a new router. i had a TP Link Archer C5 router for years (and put a bunch of them and C7s in for customers) and never had a problem anywhere until MINE started just randomly dropping wifi clients. replaced it with an Airport Extreme and haven't really had any problems since.