Cubase 9.5 noises when adjusting controls

I have a recurring problem that I now have in multiple projects in Cubase 9.5. I seem to get to a certain point in a project and then any changes made to, for example, VST instrument of effects settings (such as compression level on a compressor, or Q in an EQ) produce an audible crackle. It’s not clipping or anywhere near 0dBFS anywhere in the audio chain.

I’ve been pulling my hair out trying to get to the bottom of it without success. It’s not any particular plug-in, just any. I’ve even, reluctantly, done a complete re-install from Windows up twice now. It does it no matter what the buffer setting, and with 3 different audio interfaces I have tried now. I went through the plug-ins one by one (took ages, too long) but there was not one that showed anything in particular out of the ordinary.

I recreated the projects in Cubase 7.5 and Cubase 8 but neither of these exhibit this. It has becoming so annoying to work with now.

I have also noticed in the 9.5 projects that, at times, the Cubase user interface becomes very laggy, and sometimes the mixer does not display any levels in the mixer upon playback. Every user-interface action then becomes very laggy.

Again, it does not do this at all in the C7.5/8 versions I created.

Does anyone know what might be causing this? I would appreciate any help.

Thanks in advance.