This seems to have worked. Not sure why I had 2.0.3.94 installed in the first place though.
Is HALion Sonic SE 2.0.3.94 packaged with cubase 12 Pro installation file? I hadn’t installed HALion sonic SE separately prior to updating to 3.5.10 upon your suggestion.
I had tried installing HALion Sonic 7, but that didn’t resolve the problem.