You are correct that removing "mode=>'frac'" actually solved this issue.
We have a lot of old problems that may or may not end up causing issues and it would take a very long time to rewrite / check them all. Do you know if there is any way to test if the problem is working from the terminal? If so, I could just let it run through all our problems (on a test server) with different seeds to see if any of our problems need updating.