Hi @woz, welcome to the Cayenne Community and thank you for your bug report. Can I ask if your install of Raspbian on your Pi is running the new PIXEL update?
I suspect you’re running into the bug outlined in this thread
If that’s the case, my apologies and we’ll try to have a bug fix for this as soon as possible – in the meantime, you may want to set up VNC outside of Cayenne per these instructions from the Raspberry Pi site: Raspberry Pi Documentation - Remote Access