It's either a bug or a feature... but after ckeditor/ckeditor5#3194 the <figcaption> inside <figure class="table"> get upcasted to a <p>.
It's a "bug" as this not happened before and at the same time a "feature" as the content doesn't get lost :man_shrugging:.
You can check this in manual tests: https://github.com/ckeditor/ckeditor5-table/blob/master/tests/manual/table.html#L12-L14
is rendered:

It's fine. We don't support captioned tables yet, so the fact that this figcaption ends as a paragraph is the only thing we can do.
The famous part of documentation explains this :D
https://twitter.com/brandonkelly/status/1007404154753445888
I reported a separate ticket for captions: https://github.com/ckeditor/ckeditor5-table/issues/66
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The famous part of documentation explains this :D
https://twitter.com/brandonkelly/status/1007404154753445888