I wonder if your host moved you to a nginx server.
it has a built in cache that caused me some weird issues especially in the UBB control panel.
I had to go into cpanel and exclude ubbthreads.php to fix it.
Here is another discussion
https://www.ubbcentral.com/forums/ubbthreads.php/ubb/showflat/Number/265362/https://www.ubbcentral.com/forums/ubbthreads.php/ubb/showflat/Number/241083/
