Is this happening with all plugins, or just specific ones?
Try the following…
Quit Cubase, then locate the vstpreset subfolder belonging to the plugin, and move it out of its current location.
Relaunch Cubase, and rescan MediaBay (or at least the parent folder to which your subfolder used to belong)
Load the plugin, and try to save a new vstpreset. Does it work now? (it should have created a new subfolder for the plugin)
If so, and you already had some “old” vstpresets before moving the subfolder, quit Cubase again, and move those “old” vstpresets into the new subfolder that has just been created.
I have to jump in here and describe my path to the presets in my PC. It is different than what has been described.
Computer/C windows and programs/Users/xxxyour namexxx/Documents/VST3 Presets/Steinberg Media Technologies/…and then all the VSTs are listed that have presets
My presets are saved and able to be recalled.
And not to confuse anything or anyone, when I take the ‘roaming’ path I do find preset options but not for VST3 devices. I think the whole thing is weird, but somehow Cubase makes a distinction in these paths and that’s why they are created this way.
Solution!
I had this exact same problem - what was causing it?
I had the ‘VST3 Presets’ set to ‘hidden’ in my ‘C:\Users****\Documents’ directory!
I’m a stickler for a clean and tidy my documents folder, and had gone through all the folder attributes in there “hiding” all the folders that programs had created that I didn’t want to see
(right click on the folder > Properties > Uncheck Hidden (though I’m sure if you’ve made this same mistake you’d already know how to undo that bit!)
or perhaps you’ve deleted that folder completely in your documents directory!