Can not access `manage_access` as an admin

[gforcada]

At work we recently upgraded from Plone 5.2.x to 6.0.7 and since then I noticed that I can not go to a comment's /manage_access ZMI view anymore (to check permissions and so on).

Testing it locally with a vanilla Plone instance seems to be the case as well:

Traceback (innermost last):

    Module ZPublisher.WSGIPublisher, line 181, in transaction_pubevents
    Module ZPublisher.WSGIPublisher, line 391, in publish_module
    Module ZPublisher.WSGIPublisher, line 285, in publish
    Module ZPublisher.mapply, line 98, in mapply
    Module ZPublisher.WSGIPublisher, line 68, in call_object
    Module OFS.role, line 112, in manage_access
    Module Shared.DC.Scripts.Bindings, line 333, in __call__
    Module Shared.DC.Scripts.Bindings, line 370, in _bindAndExec
    Module App.special_dtml, line 222, in _exec
    Module DocumentTemplate._DocumentTemplate, line 144, in render_blocks
    Module DocumentTemplate._DocumentTemplate, line 245, in render_blocks_
    Module DocumentTemplate.DT_With, line 86, in render
    Module DocumentTemplate._DocumentTemplate, line 144, in render_blocks
    Module DocumentTemplate._DocumentTemplate, line 222, in render_blocks_
    Module DocumentTemplate.DT_Util, line 215, in eval
    __traceback_info__: o
    Module <string>, line 1, in <module>
    Module AccessControl.ImplPython, line 766, in guarded_getattr
    Module AccessControl.ImplPython, line 708, in aq_validate
    Module AccessControl.ImplPython, line 596, in validate
    Module AccessControl.ImplPython, line 325, in validate
    Module AccessControl.ImplPython, line 845, in raiseVerbose

AccessControl.unauthorized.Unauthorized: The container has no security assertions.  Access to 'meta_type' of (plone.app.discussion.comment.Comment object at 0x7f2d1bb81f60 oid 0x4bf1 in (ZODB.Connection.Connection object at 0x7f2d25df8150)) denied.

It's the first time I see this security assertions problem together with this meta_type... any leads? 🤔