At roughly the 1:04 point in the sequence, you have a "Single Strand Chase" dropped on the "Mini Trees" model group. For that effect, you have "Group All Arches" checked. With that checked, it creates a "virtual" string that is bufferWi x bufferHi long (400x400 or 160,000) nodes long to do the chase across. While the math in the chase effect can likely be improved, it certainly will have issues with something that size. If you ungroup, it's only 400 long which is much easier to manage.