When back end validation fires and fails, all the data entered into the form is gone (or original data is restored in the case of edited posts). I would expect that the form keeps all the data as entered before the form is saved even if validation fails, so that users don't have to fill everything from scratch. Apparently this is not a default behavior? If that's the case, suggestions on how to fix it would be much appreciated (keeping form data in cookies before it is saved into the database?).
To make it more precise, I am validating front end form with php, so I use rwmb_frontend_validate.
If the validation fails, the form clears (new submissions) or restores to original post (existing submissions). As I understand, this can be overcome by using remote validation? I didn't try it yet as the other thread you recall concerned WP back end, but will check it for the front end forms so.