Thanks for your thorough testing and reporting!
I am happy to hear the Bulk Edit feature works. You might also find that the Quick Edit rollover action also works, and is easier to use than the multi-step Bulk Edit for one item.
The MLA Bulk Edit and Quick Edit features use a different code path to update taxonomy terms – they don’t go through the WordPress wp_update_post
function if all you change is taxonomy term assignments.
In fact, the Media/Edit Media screen updates do not usually involve MLA at all, and the symptom you reported would happen for any changes, not just taxonomy terms. I regret that I must ask more questions:
- Are you able to change other fields, e.g., Caption, Alternative Text or Description?
- Do the Bulk Edit and Quick Edit functions work if you change something else, e.g., Caption or Description?
- Do you have other plugins that add features to the Media/Edit Media screen?
My system runs PHP 7.0, which is slightly less strict than 7.1 but more strict than 5.6. If further testing doesn’t yield an answer I can work with you to add some debug logging that might reveal more details. Thanks for your persistence.