Sometimes when a user saves a custom post type, WordPress saves a blank revision (see below)
I only have ACF installed as a third party plugin, I see no errors in my error_log that are related. I have no caching plugins or settings, I even increased the time-out cap for users to 24 hours. The user even logged back in and refreshed before saving.
This occurs on custom post, there are no default post types used so I'm not sure if it's a custom post type issue.
I'm hosted with BlueHost on a VPS.