We have found that sometimes when there is some kind of error in our templates or in the view code, Plone 5 returns 404 error instead of showing a proper traceback.
Today, for instance, I have registered a portlet with an incorrect name and when going to the portlet management screen I was receiving a 404 Not Found error instead of a traceback.
Yesterday I had an error in a method name of the view class and it showed a 404 error.
Is this a chameleon feature? Or am I missing something here?