Hello Danny,
(You probably realise this anyway: Hauptwerk's "Try to run Hauptwerk at real-time priority on Windows" advanced general preference can only have any effect if the Hauptwerk process is launched from Windows as "as Administrator".)
A few PCs have drivers or other system components that don't coexist comfortably with user processes (e.g. Hauptwerk) running at real-time priority. If that's the case, and if Hauptwerk performs well without running at real-time priority anyway, then I'd suggest simply avoiding running Hauptwerk at real-time priority and not worrying it.
You could also experiment with the unticking the "Bind audio engine threads to CPU cores on Windows?" advanced general preference.
You could also try running LatencyMon ( https://resplendence.com/latencymon ) whilst Hauptwerk is running with audio/MIDI active, in case it indicates that any driver/component may be causing problems for real-time audio performance.