Posted by gouessej on Aug 27, 2017; 10:40am
URL: https://forum.jogamp.org/Objects-randomly-not-rendering-on-OffScreen-Canvas-tp4038163p4038165.html

This probably solves your problem:
http://codepimpsdotorg.blogspot.fr/2010/03/java3d-offscreen-rendering-and-changing.html

I've found it by using a decent search engine (i.e not Google) ;)