Can someone please verify/confirm this issue with Plone 5.2RC3?
Confirmed the error on two other 5.2RC3 sites...same result.
Weird that it is working on demo.plone.de
@pbauer is demo.plone.de running master or RC3?
http://demo.plone.org is running Plone 5.1.5
http://demo-latest-py3.plone.org and http://demo-latest-py2.plone.org are running master of Plone 5.2.
"Reply" is also broken on your 5.2 sites.