I’ve been working with Stackable support on an issue with SlimSEO picking up page code, rather than page content. They tell me it’s something you are working on, as they can’t improve the situation from their end. SlimSEO, are you aware of this issue, and working on fixes?
I’d much prefer to stick with SlimSEO, but for now I’ve had to move to SEOPress on all my Gutenberg sites. It’s a pain to use, but it picks up the text correctly. :-/