@eric.vvf

eric.vvf → created an issue.

eric.vvf → made their first commit to this issue’s fork.

I am facing the same. But I couldn't reproduce it locally, only in Pantheon's staging environment. as @bsingh reported, there are differences in responses between cases that work and cases that don't. Happens randomly, and doesn't seem to have a pattern.

With error:

"ajax":{
            "auto_select_handler":{
               "callback":"::updateFormCallback",
               "wrapper":"media-library-wrapper",
               "event":"auto_select_media_library_widget",
               "url":"\/media-library?...",
               "dialogType":"ajax",
               "submit":{
                  "_triggering_element_name":"auto_select_handler"
               }
            }
         }

Without error:

"ajax":{
    "edit-submit--M799kaIDOac":{...}
    ...
    "auto_select_handler":{...}
    ...
}

I tried a patch to add the missing libraries (in my case: file/drupal.file and dropzonejs/integration), but the problem still persists.