I have this issue as well using the NTSC versions of the VIC-II (the issue coming up after extended uptime), and another issue to it that is related, that being only PLCC versions of the 6567R8 seem to be detected. If I use a ceramic version the board can rarely detect the chip is present, sometimes taking 6-7 power on/off cycles to get a ceramic/gold plated version to detect and it will promptly resort to not being detected on a power cycle.
I have tried with (2) different PLCC 6567R8s and (2) different ceramic 6567R8s.
I am updated to the most current firmware.