My full stack application won't run NodeJS and React concurrently - node.js

Question

Running the client server and the backend server independently will produce no errors but mongoDB exits automatically when client and server run concurrently
npm start
[nodemon] 2.0.2
[nodemon] to restart at any time, enter `rs`
[nodemon] watching dir(s): *.*
[nodemon] watching extensions: js,mjs,json
[nodemon] starting `concurrently "npm run client" "npm run server"`
[0]
[0] > roster#0.1.0 client /Users/owner/Documents/projects/roster
[0] > react-scripts start
[0]
[1]
[1] > roster#0.1.0 server /Users/owner/Documents/projects/roster
[1] > cd src/server nodemon index.js
[1]
[1] npm run server exited with code 0
[0] ℹ ｢wds｣: Project is running at http://192.168.0.4/
[0] ℹ ｢wds｣: webpack output is served from
[0] ℹ ｢wds｣: Content not from webpack is served from /Users/owner/Documents/projects/roster/public
[0] ℹ ｢wds｣: 404s will fallback to /
[0] Starting the development server...
A snippet of my package.json. I'm running npm start from the root folder roster.
"scripts": {
"start": "concurrently \"npm run client\" \"npm run server\" ",
"server": "cd src/server nodemon index.js",
"client": "react-scripts start",
"build": "react-scripts build",
"test": "react-scripts test",
"eject": "react-scripts eject"
require('dotenv').config();
const express = require('express');
const handle = require('./handlers');
const cors = require('cors');
const bodyParser = require('body-parser');
const mongoose = require('mongoose');
const app = express();
app.use(bodyParser.json());
app.use(cors());
app.use(express.json());
const uri = process.env.URI;
mongoose.connect(uri, {useNewUrlParser: true, useCreateIndex: true});
const connection = mongoose.connection;
connection.once('open', () => {
console.log("MongoDB database connection established")
})
const votesRouter = require('./routes/votes')
app.use('/votes', votesRouter);
require('dotenv').config();
app.get('/', (req, res) => res.send('hello world'));
app.use(handle.notFound);
app.use(handle.errors);
app.listen(port, console.log(`Server running on port ${port}`));

Answer 1

Add && to your server script
"server": "cd src/server && nodemon index.js"

Answer 2

That is not mongoDB.
It sounds like your two servers might be trying to run on the same port. What port do each of the servers run on?
What is in the server index.js? It is exiting with error code 0, which indicates no error exit.