CHT Problems with IPv4 distributions

Hey guys, I have a 100/40 DSL connection and the router DSL-6740C (2T2R). I always have some difficulties getting an IPv4 Adress when I want to connect with my laptops (Both Windows 10). I am 100% sure that it is a router problem, since I already tried a few things in the last weeks. Now I connected a 5GHZ WIFI bridge repeater in order to get full wifi speeds, since the shitty router only supprts 2.4GHZ which solved my problem a bit; I have assigned a static IP to my Laptops Wifi MAC adress, which solved the problem 90%. But occasinaly, the router still has difficulties to assign an IPv4 address to my laptop. I almost never have these issues with my Android phone though. On top, I also donĀ“t see my router WIFI anymore. Only the 5GHZ repeater.

So my questions are:

  1. Did you guys have similar issues with this kind of router?
  2. Is it possible to replace the original CHT DSL-6740C (2T2R) router, so I can use a new and cheap router with my CHT login informations?

Thanks!