Thanks for writing in and let me try to help here.
Currently the Client Review Site does not have annotation capabilities on mobile browsers (phones, tablets). They can play the media back and type up Notes, but cannot draw on the frames. We are sorry that the review options on mobile devices are lacking, this is certainly an area that warrants further investment and the feedback is passed along to the product team.
And unfortunately Safari is the least reliable of the recommended browsers .
A note about Safari: annotations currently do not work in the Safari browser due to a limitation that is beyond our control. For the Client Review Site, Screening Room, and Overlay Player, we recommend using Chrome and Firefox instead for an optimal experience.
He could try Chrome browser and see if he has better success.
Hope it helps,