Comments viewlet rendered twice in Plone 5.2

In our Onkopedia portal we use a slightly customized comments portlet registered as

        name="onkopedia.comments"
        for="xmldirector.connector.connector.IConnector"
        manager="plone.app.layout.viewlets.interfaces.IBelowContent"
        layer="onkopedia.policy.interfaces.IBrowserLayer"
        class=".comments.CommentsViewlet"
        template="comments.pt"
        permission="zope2.View"
    />

The standard comments viewlet is disabled.

However our comment viewlet is rendered twice. However the code of the underlaying comments.py functionality is only executed once (e.g. the has_replies() is called only once from the comments.pt template).

There is no Diazo transformation in the game here (stock Barceloneta).

Screenshot: https://nimb.ws/GnCfeu

Any idea?

Are they both in the same viewlet manager?

Do you see anything (weird) at http://path/to/page/@@manage-viewlets ?

plone.comments and onkopedia.comments are registered within the same manager but as said: plone.comments is disabled.

https://nimb.ws/TkXiAU

So both the viewlets you see are from the same viewlet manager, and you are sure that it is 'plone.comments' you see (not a duplicate of onkopedia.comments) ?

Does /@@manage-viewlets show only one viewlet?

There is only one viewlet shown within the viewlet manager view. And said: the code/template comes from our portlet (verified).

My guess is a issue with the diazo-rules. Do you still see it twice with ?diazo.off=1?

But there is no Diazo involved here...this is with plain Barcloneta

Barceloneta is 'full of diazo rules'

Again: Do you still see it twice with ?diazo.off=1 (only works in development-mode)?

Only one comment viewlet with Diazo disabled:

Barceloneta:

Plone Foundation Code of Conduct