The DHCP range won' t be the issue, if the access points are configured with static IP addresses. Can you mobile access to the router or the access points when internet stops working? You may try to...

If the traffic is not over 30mpbs, will the router still freeze? What's the result when you try wireless router mode on the 843N ? Besides, what's the model number of the main router?

Here is a beta firmware adding this function: http://static.tp-link.com/resources/software/MR200_Firmware_with_failover_function.zip

rathann wrote No, that's not what's happening. Roaming between access points happens seamlessly (I can see the BSSID of the AP I'm associated with and the signal level). It's just that I have to wait...

kuldik wrote This was true some years ago. Nowadays the roaming behavior is much more on the client side. For example iOS device starts scanning for new AP when RSSI value is <-70dBm for more than...

No need to change the subnet mask. Leave it as 255.255.255.0.