The checker was made by the user pieterix, it uses your Bookmark list so if you split it the new list also needs to be added to the checker script otherwise the caches on list #2 will not be used in the script. Reach out to pieterix via Geocaching.com and ask them to edit the checker, if you don't get a reply you can request a new checker in the challenge checker forums:
https://project-gc.com/forum/list?8