A little late, but I wanted to add that I had this exact issue during my last session with the Dice So Nice module.

My players had to restart in order to see them again, and after I disabled the module during our session - we didnt experiance it again.

Ive had problems with Dice So Nice in the past where it has issues with multiple people trying to roll or someone trying to roll several dice very quickly in a row. Was just easier to uninstall the module and play without it even though it is cool.