I have a 20,000 word post in draft currently with the same issue. I have tried disabling blocks along with the spell check in chrome. Site health is perfect, so I don’t think that is part of the issue.
@Drakz, are you running a bunch of plugins? I am running 16, but I never had an issue before and run only the bare minimum. Two plugins are caching plugins. One from Siteground and WP Rocket, I run on a Thrive theme and use 3 of their complimenting plugins as well along with Askimet & Yoast SEO.
I am also running YASR (star rating) and wondering if this is conflicting somehow.
I contacted Siteground, my host, and got no help in terms of finding an issue.
