Fred
You may have turned the display rendering settings for the scans to be something that will not show up on a white background - try the following
Try changing to a black background - do they show up then - if yes then the point cloud render color needs to be changed or use True Color or something like that
Try toggling the No Shading Mode to see if that makes a difference - try color coded intensity for example
Try toggling the See All setting in the Rendering Group of the Point Clouds Menu - I have seen clouds disappear because that setting is set to Show Inside or Show Outline?
Try changing the Point Size - do they show up then?
If you create a Cutting Plane - Vertical across the Point Cloud - can you see it in the Cutting Plane?
Apologies but without the Project I cannot simply answer the question because I have no way to validate the suggested answers - If we have the Project Archive I may be able to find the answer for you and if not I can hand it off to the Survey guys to see what they know.
Alan