This happens when i browse the forum, go to some other site and return. I always get this error. To be able to get back in the forum i have to restart the browser or create a new tab and re-load it there. Refreshing with “ctrl+Shift+R” also fixes it but regular F5 refresh does not. I also tried to delete all the site’s cookies but the problem returns every time.
This happens only with this forum. So i don’t think it’s my setup.