In most cases, it is moderation-related. Comments are typically open between 6 a.m. and 11:30 p.m. ET, Monday - Friday.
Sometimes on high-volume comment threads and/or specific stories or topics, we close and hide comments temporarily during the comment review process. Once the comments are reviewed, we unhide the comments. If the comment volume is in excess of the moderation resources available, the comments may remain hidden and the comment thread may have to stay closed.
Find more about the different types of moderation used at CBC.
In other cases, it may simply be that comments were opened in error and once we became aware of the error, we closed the comments. For more details, see the Help Centre article - "Why are some stories open for the audience to submit comments but not others?"
It is also possible that this is a technical issue. Try refreshing the page in your browser. If that doesn't work, try clearing your browsing history, emptying your browser’s cache and opening a new browser window. Type the full CBC.ca URL (www.cbc.ca) into the address bar and then access any news story from there. You could also try using a different browser.