Hi everyone,
Happy new year! 
We diagnosed a bug on the subsites hosted in our Mozilla Brazil WP Engine platform where we get errors when trying to view draft posts, those not yet published.
We believe the main problem is due to how the subsites are mapped. Since the domain is different between the admin dashboard and the preview page URL, the permissions may not be read correctly (the preview page domain may not be registering your user as logged in).
We’re still digging into this and will provide you with more info shortly, we reported it to WP Engine support to provide necessary help in this.
If there’s anyone else experiencing this bug, please let us know!
Cheers,
Geraldo Barros
on behalf Mozilla Communities Web Services team