Hardware Raytracing wasn't properly disabled or enabled in the
subdevices of the multi-device.
This construct:
foreach ( DeviceInfo &info,
(device.multi_devices.size() != 0 ?
device.multi_devices : vector<DeviceInfo>({device}))
)
was a nice trap - it was giving a copy to iterate on.
Pull Request: https://projects.blender.org/blender/blender/pulls/107989
3695f0dffc