Firebase ID Token has invalid signature (JWT)

I'm following the guide here to generate an ID token in my client via firebase and verify it in my node.js backed via the firebase SDK. This is all running from localhost without an emulator and signing-in via google sign-in.

Here's my code in the client which successfully logs a token:

const idToken = await currentUser.getIdToken()
console.log(idToken)
if (recipe.picture !== config.basePictureURL) {
     await axios.post('deletePicture', null, { headers: { authorization: 'Bearer ' + idToken } })
}

and my code in the backend which also logs the token successfully:

var firebaseAdmin = require("firebase-admin");

var firebaseServiceAccount = require("./firebaseKey.json");

firebaseAdmin.initializeApp({credential: firebaseAdmin.credential.cert(firebaseServiceAccount)});

 app.post("/deletePicture", async (req, res) => {
      console.log("authorizing user - " + req.headers['authorization'])
    
      try {
        const currentUser = await firebaseAdmin.auth().verifyIdToken(req.headers['authorization'].split(' ')[1])
        var uid = currentUser.uid;}
  catch (error) {
    console.log(error)
    console.log("Error - not a valid idToken")
    res.status(500).send(error)
  }

And it currently fails in the backend consistently with the following error:

> Firebase ID token has invalid signature. See
> https://firebase.google.com/docs/auth/admin/verify-id-tokens for
> details on how to retrieve an ID token

Here's an example of a JWT generated which is failing the signature check.

Had to downgrade to firebase admin SDK version 8 and it started working. Assuming its a fairly unique bug happening between some versions of the firebase libraries I'm using in the front-end and the backend.