Why cannot delete range in project file

I was able to edit the video file using Delete range but after 7.19 minute, the Delete Range cannot work.
It happened to this file.
Was able to use Delete Range without problem on other project files

Hi Tan,

Could you please share the project file which has the issue (Delete Range) so we can analyze further? Please also share its external data folder named in the form PROJECT_FILE_files if any.
If these files are large, you can upload them to a cloud storage site like Google Drive and send the link to us here or email us at support@atomisystems.com.