I continued investigating this and in my scenario it is related to removing meshes or disposing meshes somehow. But the lock-up requires the 2 touch gesture to happen as well! 
So, if I stop disposing meshes -or- stop touching using 2 touch gesture, the bug does not occur…
Also, when the bug locks iOS Safari, you cannot even refresh the page anymore. Also, nothing is shown in the Mac Safari’s mobile web inspector log. And when I wait for about 1-2 minutes the lock situation gets one frame rendered and then locks again…