apparently this is a recurrent issue in the Tracker List (MDL-54107, MDL-34750, MDL-41223) and in the Forum (Authentication), but no given solution is valid for my case.
I'm using Moodle 3.8.2+, with protocol https.
The problem occurs only when I try to access the website (iovolo.online) with Firefox (v. 76.0 running on Archlinux), and to make it go away I have to delete the Firefox folder altogether, which, from an User perspective, is not a nice thing to do.
So when I first access the web site, since I' m forcing the user log-in this is what I get:
It let me enter the site, but after few seconds I get the following:
Again, the problem doesn' t occur if I use Vivaldi or Konqueror web browser.
Could it be a problem with cookies or some setting in index.php?
Have a lovely day!