One or more of your promises return an exception.
You have to catch it. I would use .catch((error) => console.log(error)) to check what the exception is.
@smirnov do all your used libraries catch all exceptions? The error says that e is not defined, however there is no e in your code. Imho, the error is very stupid since it gives no information whatsoever about the location of the error (file/line)
@maruru yes, you are right, the error gives zero clue where to look for it. Of course I can't speak for every library I use, I can only do it for my promises. I used Mongoose before and never met such error.
@smirnov It's quite a new error, especially when coming from the old LTS. I also have some productive software right here which spits such a promise error on occasions, even though I handle all promise rejections. You might want to catch process.on('unhandledRejection', ()=>{}); and use your debugger's trace to find out what's going on...