In my experience it depends on the blog/article. You aren't always able to see the full article without logging in and you get a limited number of free articles when signed in.
I have yet to run into an article limit without being signed in. I hit the limit on the reg as many tech articles that turn up while troubleshooting are on Medium these days. Maybe the problem is signing in?
Yes the problem definitely is related to signing in. Ironically you can view more if you do not! However, I have run into a few blogs/articles that require sign in to read.