I have MetaBox 4.13.4 installed and am using the Gutenberg plugin. I created a metabox that functions perfectly when I set the context to "normal" or "advanced". However, if I set the context to "after_editor", "after_title", or "form_top", the meta box does not appear on the page at all. The meta box does appear if I switch to the classic editor.
Unfortunately, Gutenberg doesn't support contexts. It has only one place to show meta boxes. So, please just remove the contexts param from the meta box settings.