MERN Backend Bug Fixes

My Node.js + Express backend has started throwing intermittent server-level errors and several API endpoints are no longer responding as expected. The React front end is stable, so your focus will be purely on the backend layer of this MERN application... (Budget: $250 - $750 USD, Jobs: AngularJS, API Development, API Testing, Backend Development, JavaScript, MERN, Node.js, NoSQL Couch & Mongo)