If you are using WPA2 encryption on your WiFi, change the pass phrase and pick a good long random sequence of characters including letters, numbers, punctuation and other symbols on the keyboard.
Disable WPS and UPnP in the router.
On any Windows 10 PCs, disable the stupid facility to tell your contacts the credentials of your WiFi network(s).
Make sure there are no trojans on your computers that are sending information to the enemy. I count Windows 10 as a potential trojan.
Check what MAC addresses are connecting to your network. These should be listed in the router's network pages and possibly its log files. The first half of the MAC address will indicate the type of network chip and possibly the type of device that is connecting.
Use MAC address white list or black list filtering in the router to allow only your devices or block alien devices.
Turn off the WiFi network during the night. many routers include settings to do this automatically.
Make sure there is no port forwarding configured in the router that is allowing access that way rather than by WiFi. Also make sure the DMZ and remote management of the router are disabled.
Is the NR676 controlled using infrared, WiFi or Bluetooth. If it is IR, then it is possible that a neighbour may be triggering your unit unintentionally when they control their unit. If it is Bluetooth, could a second controller be paired with your unit?
Finally, although I mentioned it first, changing the WiFi pass phrase should be done as a last step if WiFi is the source of the control. However, if a good random pass phrase does not stop the problem, I would be inclined to suspect IR. Bluetooth should not normally be an issue as most systems require authorisation of some sort to allow pairing to take place.
I hope this helps.