If you have updated to Catalina on a Mac then that operating system introduces additional security requirements which can prevent the HUD from displaying if PokerTracker 4 doesn't have permission - see
this guide for how you can re-enable the HUD. If you are on Windows then please
enable logging, reproduce this problem and then send your log file to us in a
Support Ticket. You can access the 'Logs' folder with the log file by clicking 'File --> Open User Data Folder' in the main PokerTracker 4 window and depending on your Windows settings it will be a text file called 'PokerTracker4' or 'PokerTracker4.log'.