WordPress Preview Button Actually Saving Data

Greetings,

We have a problem that we've isolated to an interaction between Meta Box and one of our page templates. We're continuing to troubleshoot things on our end, but thought we'd post here in case anyone has any insight into the problem.

Here's the situation: one of our page templates, named Landing Page, includes a series of Meta Box fields for some content and display options. One of our editors noticed that, when they are editing such a page, clicking the WordPress preview button to review their changes is actually changing the page's data, even if you don't change Meta Box information. That is, if you only change (for example) the page's title, then click the preview button, the entire page is saved for real and the live site displays the new title. Even the toast notification the WP shows when the page is saved pops up in the lower left, so the core wp_update_post function appears to be running in a way that it's not supposed to.

We know it's a Meta Box interaction because we removed the fields from that template (by removing it from the array returned by our custom rwmb_meta_boxes filter) and without the fields, the WordPress preview button works as expected (i.e. the currently live site remains unchanged).

We're running WP 5.4.2, Meta Box 5.3.3, and Meta Box AIO 1.11.16. We do use Gutenberg as our editor. Any help leading us to find the cause of this problem would be most appreciated.

Thanks,
David Dashifen Kees
Senior Full Stack Developer
University Information Services
Georgetown University