We just checked this on a fresh install of Windows 8.1 - all updates. RM Series Mixers appear and operate in UC 18.104.22.168558 as expected.
Strongly suggest doing the following:
- Turn off mixer
- Use Programs and Features in Windows Control Panel to uninstall Universal Control.
- Open C:\Windows\Temp - delete everything in that folder (that Windows will let you)
- Windows Key + R to bring up Run Command, type %appdata% and navigate to PreSonus folder and delete Universal Control folder.
- Empty your trash
- Make sure your system is up to date, run Windows update until it tells you your system is up to date.
- Update VCRunTimes - https://support.microsoft.com/en-us/help/2977003/the-latest-supported-visual-c-downloads
- Install both 64-Bit and 32-Bit Visual C++ Runtimes just to be sure.
- Install Universal Control 22.214.171.124558
- Reboot a 2nd time after install is complete
- At the desktop Open Universal Control and turn on your mixer
Mixer should appear in Universal Control.
If not open a support ticket at https://support.presonus.com for further assistance and include everything you did here so they can assist.