Here is all the information I discovered, so that it may help someone else. I strongly suggest you read through it all first, before following the steps (and back up your machine to be on the safe side).
CAUSE:
XML Settings File Had Stopped Updating
SOLUTION:
Reinstallation of Synthesizer V and the explicit removal of the Application Support folder (see below)
CHECK:
I cannot guarantee this is your issue, or that this solution will work for you. To check that you are experiencing the same issue, go to [Your HD] → Library → Application Support → Dreamtonics → Synthesizer V Studio → settings and try to open and edit the file with TextEdit (i.e. a native Mac application). In my case I got the following error:
Uninstall Synthesizer V - remember to deactivate it and all your voices first! I uninstalled all the voices (check you have all the necessary files & licences needed to reinstall everything)
NOTE: I used a free program called AppCleaner, which finds associated files when you uninstall Mac apps. You will need to install this before deleting the Dreamtonics app if you want to do this same. It found all of the following (I removed them all):