Usually if you have it.
They will provide a item in your cpanel to select.
The icon might be labeled cache or nginx
When you open it there will be a spot to exclude files from the server cache along with other items for caching.
Just add ubbthreads.php to the exclude list.
It will stop caching that file.
If not then you probably need to contact the host and have them exclude that file from the nginx cache.
