Would this thread help? (sorry, is it against the rules to quote info from other forums? If so, please delete this):
https://www.guineapigcages.com/forum/threads/10935-Coroplast-measurements
Apparently, there are two solutions:
1. Measure the correx slightly smaller, as to fit between the connectors, not between the grids. You end up with a tiny gap between the walls of the correx and the grids though
2. Swap the bottom connectors for cable ties instead
Thanks for starting the thread! Otherwise, I wouldn't have known of the issue in advance, and sourcing correx is a true nightmare for me, so I can't afford any mistakes