Matrix Issues After Upgrading from 2.4 to 2.6 Running into some issues with matrix fields after upgrading from 2.4 to 2.6.

The matrix in the site includes a whole bunch of block types that are used to build row-based pages (e.g., Intro, Profile, News, Text, etc.).

When creating a new page everything works just fine at first. However, when you insert certain block types into the matrix, suddenly you can no longer reorder/collapse/add blocks in that matrix.

I notice that when it breaks, the following error pops up in the console:

Uncaught: TypeError: Cannot read property '0' of undefined - velocity.min.js


Anyone run into this or have ideas to what this might be? I can't seem to find a commonality between the blocks that cause the error and am not sure where to go with this. 

Note: this particular matrix config has a ton of fields (we've had to extend the php memory limit etc. when saving changes to the config).

Tks in advance!
Craft 2.5 changed from Redactor I to Redactor II, so chances are you just need to update your Redactor configs to the new format: https://craftcms.com/support/redactor-ii-configs