Paragraph forms are not displayed

This is a little confusing, so perhaps a sort of visual illustration:

Say I have a Paragraph Type, "Fnord". A Fnord has a single text field. And say I have a Content Type, "Foo." A Foo node has an image field, and a revision reference field allowing an unlimited number of Fnords. If I do not have the Field Group module installed, then a Foo edit form works as expected: I see the image field, and I see an empty Fnord item with an empty text field. I can fill in the text field, add another Fnord, and repeat.

If I *do* have the Field Group module installed, however, the Fnord's text field disappears. Everything else is still there -- I can add, delete, and reorder Fnords -- but the text field is gone from all the Fnords.

I've tested this in 8.x-1.0, 8.x-3.0-beta1, and 8.x-3.x-dev, all with the same results. The module need only be installed -- I don't have to have any field groups in use on the entity form in question.