Not really sure what's happening with galaxy app booster. But to regain your storage, you can give this a try: Go to Settings - > Device Care - > upper righthand corner press on three dots - > Storage booster - > You can delete duplicate images or saved apks (if any). Now most important, you have to enable autodelete unnecessary data. Click on that, and schedule it for every midnight. Wait for 12 am, you will get notified that data is being cleared. I'm almost 90% sure you will regain back the space.
