Did you perhaps reinstall AudioBox VSL 1.3 after installing 1.8.3?
The VSL software is not compatible with Mac 10.11 or higher. Installing it will kill VSL audio entirely.
Please open the DMG that the 1.8.3 installer came with, in there is an uninstaller.
Turn off your 44VSL, run the uninstaller, reboot after the system is done.
Then reinstall UC 1.8.3 and after the 2nd restart, plug in and turn on your 44VSL.
That should do it.
If that still doesn't work. Then contact support at http://support.presonus.com