Preview option doesn't work for custom post types

We have a custom type "Shows". When editing, the preview button doesn't work. The "view post" button on top works fine.
We have a custom type "Shows". When editing, the preview button doesn't work.
I've tried to re-save Permalinks settings, tried to deactivate Domain Mapping, but this didn't help.
I will also do a plugin/theme conflict test after hours.