I have an issue that seems to occur in Safari in particular, both on the Mac and the iPad. I don’t know whether the theme (GeneratePress Marketer) or Gutenberg is to blame, but have found no mention of it in a search for Gutenberg-related bugs.
What happens is that I load a page, and the caption for a picture appears overlapping the text in the block below it. If I reload the page, it lays itself out properly.
The page is rendering in amphtml, incidentally, via the official Amp plugin, in case that is another possible cause.