This is the second time I have seen this bug reported (project file is all NUL characters). This is very unfortunate, but we have no idea yet what is the cause or how to cause it. It is very unlikely due to updating the Shotcut software; that is most likely a coincidence. In Windows, you can turn on Backups for the folder where you keep project files to try to make recovery possible. That is a strong recommendation for the documents and project folders on any computer OS.