At this point I have tried everything I know to fix the issue.
Issue: preview only works right after a custom posts is loaded or updated. If you make any changes or hit preview twice without clicking update the preview 404s. On pages and posts preview works fine.
We were using the ACF and CPT-UI plugins and roots theme. I have turned off all the plugins, switch to the 2014 theme, add the CPT manually, and Update WP core.
We have a lot of Custom post types in our site and rebuilding would be a huge pain.
Has anyone dealt with this issues? Anything helps.