I think Nabble will need you to post the URL of a forum where you see this happening so they can investigate the issue.
There have been cases where similar problems are caused by non-standard code in the site in which the forum is embedded, so it might be a problem with the host site rather than Nabble.
There have been other cases where the problem is caused by the browser used to visit the site, so it would also be helpful to say what browser you are using.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.