Unlike an access point, an extender may or may not use a separate, unique MAC address to communicate to the router on behalf of each device. Therefore, in cases where the extender does not pass through the unique device information, the extender (and any devices connected to it) will be handled as one device in Router Limits. You can typically avoid this problem by hardwiring the wireless extender. Powerline extenders are also a good alternative.
SEE ALSO: Duplicate Entries For The Same Device