The car is not visible on different segments. What to do? What is the problem?

Question

Computer networks

There is a network:

k5 >> << wi-fi router (k1.k2) -- hub -- hub -- wi-fi client >> << wi-fi ap -- hub (k3, k4)

k5 and k1 see k3 and k4, but k2 and all the others connected to the router via LAN are not. The router itself pings k3 and k4. From the LAN router, only k1 sees k3 and k4.

Answer 1

Default gateway is configured correctly everywhere? Does everyone have the same subnet? Is it one ethernet segment? Wifi client is also a router?
Show the subnets and selected segments in the figure, otherwise it is not entirely clear ...

Answer 2

Without specifying routes and networks, it is difficult to answer the question. Describe addressing and routing in more detail. If there is a NAT somewhere, please indicate it.