Missing Characters and Opaque Error Message

What device are you uploading to?

I remember this being a problem on early Native IDEs when used with new Espruino firmwares, but I thought the most recent one had fixed this.

Is there any chance you could just use Chrome/Edge and espruino.com/ide? Should work fine on Windows 10 and it may solve all your communication problems.

Does the software report where an error was on its minified code instead of the code as written?

If you upload minified code then that's all Espruino has to go on, so it'll report errors in that. Usually it'll be normal though