Why is my PC no longer adding tracks to iCloud

My iTunes Match subscription is active but suddenly my PC has stopped uploading new tracks to iCloud so they no longer appear on my iPhone or iPad. In my account there is an option to Add This Computer to iCloud but all that button does is ask me to download the latest version of iTunes. I am already running v12.3.3.17 however all reference to iTunes Match seems to have disappeared from the menus. I have not signed up to iTunes Music so I have no idea what is going on. Help!