Im having the same issue and just got this message from tech support:
"This is a known issue with the latest release of Studio One 3.3.2. We are logging these issues and looking for a fix to be released in a future update. If you need to use your MCU Pro there are 2 options:
1.) You can use the MCU Pro in HUI mode with Studio One 3.3.2. However, the usage of the MCU in HUI mode within Studio One may not provide the best user experience. For this reason I recommend the second option.
2.) You can download the previous version 3.3.1 from your my.presonus.com account. My products > Software > Studio One 3 Professional and under the installer you will see "View Previous Versions" and you can select version 3.3.1 from the drop down menu.
I apologize for any inconvenience this may have caused."