How to debug my really slow resolver connected to Firebase Realtime Database?

Question

I have an graphql server connected to my Firebase RTD and deployed on heroku.

When I run my server in heroku the request to reservations resolver takes forever and eventually the Playground yells Unexpected token < in JSON at position 0

I suspect this is a timeout from Firebase, but how would I go about debugging this? (Heroku logs nothing about the error).

You can try the server for yourself: https://filex-database.herokuapp.com

The specific query that's causing me trouble is:

query {
  reservations {
    code
    name
  }
}

const db = require("../datasources/db");
const masterlist = require("../datasources/masterlist.js");
const getById = (key: string, id: string) =>
  db[key].filter((item) => item.id === id)[0];

const firebaseQuery = (context: { firebaseClient }, endpoint: string) => {
  const finalEndpoint =
    endpoint.charAt(0) === "/" ? endpoint : "/".concat(endpoint);
  const baseUrl = "/workshops";
  return context.firebaseClient
    .database()
    .ref(`${baseUrl}${finalEndpoint}`)
    .once("value")
    .then((snapshot) => snapshot.val());
};

const Query = {
  workshops: () => db.workshops,
  workshop: (_, args) => getById("workshops", args.id),
  options: () => db.options,
  option: (_, args) => getById("options", args.id),

 // this resolver is causing me trouble
  reservations: async (_, __, context) => {
    const data = await firebaseQuery(context, "/applicants");
    return Object.values(data);
  },
  reservation: async (_, args, context) => {
    const data = await firebaseQuery(context, `/applicants/${args.id}`);
    return data;
  },
};

module.exports = { Query };

EDIT: I made another simple server using the same technology and only delivering that resolver and it also timesout (everything works fine locally though)

http://apollo-testing-gonzo.herokuapp.com