In Automattic/jetpack#11250 I raised a problem with a PHP Notice appearing during display of the Form block. This post is a test to see if the problem occurs when the post type supports ‘author’
Could it be the author thingy?
I imagine the problem will go away with the next update to the oik-shortcodes plugin, where I’ve added post type supports author to a number of post types in order to support my own shortcodes/blocks that use the author data. See bobbingwide/oik-shortcodes#61.
Manually adding post type support using oik-types appeared to make the problem worse! In some cases the Notice was issued before Headers. It did however seem to fix the post created for the Form block, once I’d saved the post again. Do we need to check the value of post->author?