I think I solved it!
First - the white noise comes when the talkback switches off automatically. If I turn it off before pressing play, it’s fine.
Now for the offset - it seem to come from the interaction between the built in USB driver of the Samson mic and the Generic Low Latency ASIO driver and VST Connect Performer. It starts to accumulate latency the longer it is in use. We’ve solved the problem by my switching from the Generic ASIO driver to ASIO4ALL and back again in the VST Connect editor. It seems to reset either the mic or the Generic ASIO driver, and we’re able to work. I’m recommending that he invest in a USB audio interface and a better mic.
We managed to do several takes today.
But now the bad news. When I hit logout from VST Connect, Cubase immediately crashed. I’ve captured the output of the window in a text file - for some reason there are no Cubase crash logs showing up in /DiagnosticReports. It’s too long to paste into this window, so I don’t know how to share it.