Could you try this solution:
1. Go to forum where your thread is;
2. Open title and properties for this forum;
3. See if you selected the Default page
If not selected than you should select the page where the forum is displayed.
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items