Warning: Invalid argument supplied for foreach() in taxonomy_field_formatter_view()
As per this post, this warning can be eliminated by editing the field on each file type which is having a field and unchecking Override in WYSIWYG (at /admin/structure/file-types). This happens because term reference doesn't support overridable in the WYSIWYG.

This issue at Drupal.org: #2062721: Add a white list of file fields that can be overwritten when the file is added in the wysiwyg, aiming to solve that issue. At time of writing, there is still some patch which is in Needs review status.