I think this started happening after I downloaded pre-release Version: 1.72.17474. Which fixed a related problem.
The debug output was
Starting Debugger Server ...
Listening to Xdebug on 0.0.0.0:9003,[::]:9003
Debugger Server is running.
Auto-attach to process ' PHP.Debugger.Systray.exe' on machine 'GEORGESURFACE' succeeded.
Verbose logs are written to:
WARNING: Processing source-maps of http://localhost:54380/js/tests.js took longer than 11000 ms so we continued execution without waiting for all the breakpoints for the script to be set.
The warning was repeated for every .js file but not the PHP file.
I guess it's not critical!