I have seen the same thing as you (showing connected in Devices with Cubase 8, 64 bit), but the IPad not connecting. Not every time, though.
In the FAQ, it does say that the SKI extension must match the Cubase version (64 bit extension with 64 bit app). In my case, I’m not running the 32 bit version, so that wouldn’t be an issue. Could be with you.
The one thing that I’m wondering is if it could be attributed to a slow wireless connection. I’m using my home wireless network for connection, and where the music computer is located is in an area with weak signal, and as a result, not particularly zippy speeds. Now, it shouldn’t be an issue, but timings could have changed in the startup with Cubase 8 (I’m in the industry, and have seen stuff like this before…)
I was going to try a peer-to-peer connection, or drop a router right in the room to see if things improve. Haven’t done it yet.
The other thing would be to complain in the main Cubase thread, to see if anyone is working OK. If they are, they wouldn’t look at this group.