This is due to non-persistent tapdevs. Tap needs to be created first, then as the autobuilder user, vncserver started. Setting as a bug to remind me to set this up as an init script prior to our next round of reboots.
This just needs an init.d script to bring up tap devices and vncserver. I should have this done in a few days.
Any update on this bug? I thought this was fixed?
The tap dev scripts were not part of my set up procedures and so were not installed on the new builders. There were also some Debian specific changes that needed to be made. The tap devs and X session are now initialized on boot.