After some tinkering I discovered that this seems to be related to the camera setting, as going to Advanced Camera Tools and resetting the camera, the issue goes away:
Thanks for the info, yes I have got Vray, and sorry I didn’t find the previous posts myself! I wonder if the issue still occurs if Vray is not installed but the user selects (say) the 35mm camera using the Advanced camera tools (in which case it really is a SU problem not a Vray problem…?