There was a regression introduced in z3c.form 3.2.3. It seems to be affecting many people for some time. Here is an example of a issue that was just reported on collective.documentviewer:

The fix

To fix, downgrade z3c.form to 3.2.1. In your buildout, pin the z3c.form version:

z3c.form = 3.2.1

Then, run buildout, restart your instance.


The bug is fixed here:

We're just waiting on a new release.

This is affecting Plone 5 latest and Plone 4.3.6.