PHP version: any
Xdebug version: any
VS Code extension version: 1.19
Your launch.json: irrelevant
Xdebug php.ini config: irrelevant
Xdebug logfile (from setting xdebug.log in php.ini): irrelevant
VS Code extension logfile (from setting "log": true in launch.json): irrelevant
Code snippet to reproduce: irrelevant
When you just started the debugger, it already shows "RUNNING" in call stack heading, even if no clients connected. And it will remain in "RUNNING" state, when last client disconnects.
This makes it impossible to distinguish a long-running code from terminated session.