Hi Cort,
Would it be possible for you to try reproducing this in a new project with minimal assets and then privately sharing that with us? If you can pass us a reproduction case it should be much quicker to look in to as it definitely sounds like there’s a bug there. We did recently fix a few material function issues for 4.14 so it could be related, but it’s difficult to offer suggestions without getting the assert up in front of me.
Thanks,
Chris