Thanks for the info. Ok, so file ownership root:everyone and file permissions 660 are as expected, the SELinux context as well. However, the error "owner died" is really strange! Never saw that before.
Can you switch to root in your terminal app? (You would need to allow root for apps in the developer options, restart the terminal app and enter the command 'su'). If yes, try deleting the file as root and show me, what happens. If not, please show me the error.