I’ve just run into this issue on a site with a pretty standard Gutenberg install and narrowed it down to this plugin, which has just added a bunch of block-related features in version 4.0: https://ww.wp.xz.cn/plugins/widget-options/
Could you maybe have it as an off-by-default feature with some language explaining you need to verify your theme actually outputs featured images accessibly?
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This reply was modified 6 years, 9 months ago by cbirdsong.
