I have High Sierra 10.13.6 on a mid 2011 iMac and every time I try to load the drivers I have the same problem.

I follow the process below
1. System preferences: security and settings - allow apps from apple & identified
2. install RME Driver
3. Restart
4. System preferences (Again) : Click on the new button, which allow RME driver to be installed

The problem is that in step 4 the dialogue 'System software from developer RME Gmnh...'       'ALLOW'
appears for a second or 2 and then simply disappears. Total Mix and the Fireface Settings apps don't work.
I have done clean installs as well as installing over the existing file...

I'd love it if there was anyone out there who can help ...