I fixed the probolem on my discussion by using these steps.
1-I changed the discussion from graded to ungraded and set an "available from" date to a few minutes in the future.
The discussion opened properly as available on my Canvas page.
2-I changed the discussion back from ungraded to graded without changing the "available from" time and the discussion remained available on my Canvas page as a graded discussion.
Fingers crossed nothing goes wrong.
