Flask with firebase_admin async firestore client runtime error: Event loop is closed

Question

When running a Flask application in combination with an async firestore client, a runtime error 'Event loop is closed' appears the second time loading the page.

Example app:

import firebase_admin
from firebase_admin import credentials, firestore_async
from flask import Flask

cred = credentials.Certificate('credentials.json')
firebase_admin.initialize_app(cred)
db = firestore_async.client()

app = Flask(__name__)

@app.route('/')
async def hello_world():
    await db.collection("product").get()
    return 'Hello, World!'

if __name__ == "__main__":
    app.run(debug=True)

I tried to run this application, which works correctly until the second load of the page. When running the app with a wsgi worker, the error sometimes appears and sometimes does not. I also tried creating a new client for every request, but the issue remains.