Check this in Mojave:
SysPrefs>Accessibility>Privacy>Microphone: Make sure Studio One app is in there and box is checked.
SysPrefs>Accessibility>Privacy>Microphone: same drill.
I'm no longer using Quantum so I don't recall if Quantum's software package needs to be there as well. I'm using Apollo and my UAD engine is in those places and is checked, so worth adding. But essentially, this goes for ALL software that manages audio...put them in there.
This is a major system change in Mojave and PreSonus isn't blasting this out to users. This problem cost me a day of frustration and a session. Hope this helps.