When a richtext field is used in a compound and that compound is used as a content block the ckeditor is unable to open dialogs. This means that when clicking the externallink or table button the background gets the dialog overlay but the actual dialog itself is missing. This issue only occurs when logged in as an editor. As admin everything works fine.
I was able to reproduce this issue in the 10.1.2 and 10.2.0 archetype. The 10.2.0 archetype project was added as an attachment to this issue.
See also Hippo Community thread https://groups.google.com/forum/#!msg/hippo-community/GOWgqiabu5g/qcZafGPGAwAJ
The cause turned out to be the fact that an editor could not read the hippostd:html subnode of the compound's prototype.