Pagination for custom post type breaking after p25

hi,
I have customised the simple-mag theme for a client and added two custom post types in order that she can tailor content by city (sydney and melbourne).

I’m usind pre-get posts to check for a cookie that set the visitors preference for the city.

I also have a page template for ‘all posts’ which has pagination.

For some reason, the pagination works up to page 25 and then throws a 404 error.

Does anyone have any ideas?
https://eatdrinkplay.com/everything/page/25/ – working
https://eatdrinkplay.com/everything/page/26/ – 404