LoggingDebugSession does not appear to ever create a log file (for trace:true launches) when running from vscode. Running standalone under node, or vscode-electron-run-as-node works fine.
I first ran into this issue in https://github.com/justarandomgeek/vscode-factoriomod-debug, which creates the trace log in path.join(os.tmpdir(), "fmtk.log"). Testing with Mock Debug, I was unable to find where its log should have been, and thus unable to determine for sure if it was creating it or not (but I believe not).