Installed V6 box on Friday, connected to the hub via wifi from our front room. The TiVo box is now in the back room connected to the hub via Ethernet cable. Initially I could connect from V6 to TiVo to watch shows recorded on the TiVo. Now I keep getting C423 error and can only connect if I reboot both boxes, sometimes repeatedly. The V6 also keeps getting a black screen with sound only. Have rung customer services who didn't seem to know that the boxes connect (!) and can't send an engineer until next Saturday!
Very similar setup here (powerlines where you have ethernet but wi-fi to my V6) and I had similar problems of the boxes losing each other and requiring a reboot.
The solution for me was to improve the wi-fi signal to the V6 by forcing it on to the 5GHz band. That may work for you, I:
Logged on to the SuperHub 3, went to Advanced Settings -> Wireless -> Security and gave the 5GHz band a different name to the 2.4GHz band. I just stuck a "5" on the end of the SSID for the 5GHz band.
Then on the V6 in Help and Settings -> Settings -> Network (forget what’s next…) I told it to connect to the 5GHz band I named in the previous step
That may help if your V6 is close enough to get a reasonable 5GHz signal. If you can’t see the 5GHz SSID on your V6 or it doesn’t help, or makes things worse then sorry to say it won’t help you. Best to go back and set the 5GHz SSID to the same as 2.4GHz as you found it on the SuperHub 3.
If the wi-fi signal strength to the V6 is low (say <50%) as shown on the V6’s network screen then you may need to try powerlines to give it a better connection and stop the boxes losing each other.
Just my opinion and experience, I don’t claim to be a great expert!