To reproduce:

1. In Site Administration. Set "Force users to log in" (forcelogin) to yes.
2. In Site Administration > Users > Permissions > User policies enable "Auto-login guests" (autologinguests).
3. In Site Administration > Plugins > Authentication > Manage authentication > Set "Guest login button" (guestloginbutton) to "show".
4. Create a category with permission "moodle/category:viewcourselist" enabled for roles guest, authenticated user, and authenticated user on site home.
5. Create a course within that category, enable guest access on the course enrolment method.
6. Add a page module.
7. Copy the link to the page module
8. Open private/incognito window. Paste the link into a browser that is not logged in to the site and has never visited the site before. 
9. You will receive a "This Activity is Currently Hidden" message even though you can access the activity. 

This will happen on the first visit, but not thereafter unless you clear history and cookies on that browser.