File still in use although project is closed

[Austin]

See:

File lock(release) on imported video files [Windows]

Choose close twice. The Shotcut engine does not try to keep every file in your project open because then it could run out of maximum file handles or use too much memory. It only keeps around 3*(number of tracks + 1). There are separate counters for A/V clips versus still images. It is not easy to predict as it is automatic based on N most recently accessed.