I've created an example repo to demonstrate https://gitlab.com/frehner/sys-rxjs

But here are the issues I've found and documented -- however, I think there's a chance that they all stem from a single issue that appears to be some sort of race condition in SystemJS. I'm not sure though.

Errors received

There are several different errors that can be received, and none of them consistently. Sometimes both finalizes are called, sometimes only one is called, and sometimes there's an error and the code isn't even executed.

1. TypeError: Object(...) is not a function.
   • Can be found in Firefox v72 on MacOS, and more rarely in Chrome 80 on MacOS
   • Points to this line Object(rxjs_operators__WEBPACK_IMPORTED_MODULE_1__["tap"])((x) => console.log('module', x)),
2. Mod1 finalize is not called
   • Can be found in Firefox v72 on MacOS with Disable Cache unchecked
   • Can be found in Chrome 80 on MacOS with Disable Cache checked
   • Can be found in Safari 13.0.4 in both cache situations
3. Uncaught (in promise) TypeError: rxjs.interval is not a function at (index):46
   • Can be found in Chrome 80 on MacOS with Disable Cache unchecked