Okay, now let’s try something different… Please open a command window by clicking on the windows button on your taskbar, then type the 3 letters C, M and D, then Enter/Return and into the now popping-up window copy and paste the following line
"C:\Program Files\Steinberg\Dorico5\VSTAudioEngine\Components\vstscanner.exe" -p "C:/Program Files/Common Files/VST3/Steinberg/HALion Sonic.vst3/Contents/x86_64-win/HALion Sonic.vst3"
Please make sure you really get everything from the first quotation mark until the last one. Then press Enter or Return.
How does that then behave, is the vstscannermaster running for some time and then disappears? How about vstcanner processes, are they coming and going ?