When utilizing Discussion Board topics in Canvas, you may experience a situation where your discussion topic becomes closed after the availability date becomes true. This is a normal situation.
However, if you have multiple Assign To rules, these can no longer be used to extend the availability dates after the topic becomes closed.
This is a bug in Canvas which Canvas support engineers are working on a fix. A current workaround is to remove all 'Assign to' rules and only leave one assigned to 'Everyone'. This will then allow you to re-open the discussion topic by updating the 'Until' date that you may allow the topic to be open.
If you have any questions or issues, contact Technology Support Services
419-434-4357