Moving threads - some forums are not available?

We recently upgraded to 10.3 and in the new UI when we attempt to move a thread, some of our forums are not displayed in the drop down menu to select which forum to move to, and in some cases forums that are visible and joinless, will display an error message saying (author of thread) doesn't have permission to post in that forum, even though there is no issue with posting permissions. 

Is there a setting in the new UI to make the forums discoverable?

Thanks