On current master demo content (0.8 just released):

1
Error: Attribute label not allowed on element button at this point.
<button type="button" aria-expanded="true" label="Open section: Status &amp; Visibility" ...

this is because the panel body Button receives a label prop that should be aria-label

2
Error: Element figcaption not allowed as child of element div in this context.

<div class="blocks-editable"><figcaption contenteditable="true" class="blocks-editable__tinymce mce-content-body" aria-label="Write caption…" id="mce_7" data-is-placeholder-visible="false">

3
Error: Element div not allowed as child of element span in this context.
<div class="editor-visual-editor__block-edit"><span class="wp-block-button"><div class="blocks-editable">

4
Error: The scrolling attribute on the iframe element is obsolete. Use CSS instead.