It may have been helpful to show a screenshot. I am not familiar with this error in Shotcut specifically.
A common error in Shotcut is when a source file is moved/renamed/deleted, it will show “Invalid” in the preview window when the playhead is in that location. There is a built-in utility upon startup to fix such errors. Related documentation here: Project Management
Your issue may be a Windows-only related topic possibly with your computer hardware.
