Completely blank page affecting some users

I'm at a loss with an access / permission problem

I've published a report in a workspace that has a few distribution and security groups added in the Viewer role, so the report has the same (Read) permissions granted to the end-users

The source dataset is in a different workspace, and has read access granted to the same groups

The source dataset has RLS and the same groups have been used to place users into roles

Having done all that, some users see the report while others just see a completely blank report page

I have now idea where to look to solve this - any tips?