Keep pressing the reset button more than 10 seconds. If nothing happens, it should be faulty.

WA850RE only has range extender mode. If you want to use it as AP, during setup, choose Set SSID and MAC Manually. Input the SSID and password you need and create a fake MAC address. It may work but...

As I know, when you restart the router and plug the USB driver to another USB port, it will re-scan. You may give a try. Obviously, it is not quite convenient but not sure if they will add the...

Firmware Version? Are you using the same SSID and password for powerline extender and main router? Since the ipad mini works OK all the time, the extender should work OK. Try to change channel on web...

Not sure as it is not in the compatiblity list of W8968. You are a reseller? You may test for the customer and his dongle? :)

Your MR3040 is V1 or V2? If it is V2, maybe you can try to get a beta firmware from TP-LINK support team and test if it works. http://ticket.tp-link.com/index.php?/Tickets/Submit