Some device/browser combinations have been unable to access the forum. We believe we have fixed the problem. (No feedback function, i.e. “If you can’t read this, send a reply”.)
The apparent cause: to migrate users from CSGnet to Discourse we used a plugin to Discourse. A Discourse update appears to be incompatible with that old plugin. Rupert removed the plugin. Some users who reported problems now have full access restored.