In nodeDebug.ts, this comment exists at line 431:
/*
this._node.on('beforeCompile', (event: NodeV8Event) => {
this.outLine(`beforeCompile ${this._scriptToPath(event.body.script)}`);
});
this._node.on('afterCompile', (event: NodeV8Event) => {
this.outLine(`afterCompile ${this._scriptToPath(event.body.script)}`);
});
*/
After this comment, the sourcemappings are incorrect, making it very hard to debug. You can see this by building and using the sourcemap visualizer: https://sokra.github.io/source-map-visualization. There shouldn't be several mappings on these lines, on individual letters, etc:

It looks like the empty line between those two blocks is removed, and the subsequent mappings are all off by a line. Looking at the code, I have no clue why that would happen.