In reply to Øystein.

I'm using Dreamhost, which is supposed to offer a pretty good WP environment. I use shared hosting because I don't get that much traffic on my site. My plugins are pretty vanilla, and I've tried the usual workarounds of disabling all plugins, clearing my browser cache/cookies, using different browsers, etc. It's usually quite random, and I could work around by using the Classic Editor plugin to start a post, then switch to the block editor, but now that doesn't work either. Creating and posting using the iOS apps or the old Open Live Writer work fine, obviously, so I've been using those.

If you think that it's the development/hosting platform, can you provide any direction in diagnosing if that is the problem? Should something be logged when this error occurs?