Cannot access to client device via browser using ip address

[thegroupad]

I have a router IP as 192.168.3.1 and wired connect to a switch. An AP(a) 192.168.3.2 wired connect to the switch as well. Another client 192.168.3.3 wireless link to the AP(a). Behind the client there is an AP(b) wired connect to it. They are connected and have internet.

I can access the client 192.168.3.3 via browser when connected to AP(b) but cannot access the client when connected to router and AP(a). I am able to ping the client.

What is the problem?

[pieterh]

this can depend on the subnet mask and as a result of this routing.

the client has a wireless link to the switch and the router,
and a wired link to an access point (and devices behind this)
but both addresses lay within the same /24 network

when the router is reachable, the interface facing the router will be used for the default route
and the client can only reach the AP(b) as this is directly connected, but not the devices behind this AP(b)
when the wireless link is disconnected, the router is not reachable as default gateway and all packets are send using the wired link