Syncing with background fetch

Is anyone aware of a way to allow a flexible sync realm to update and push local changes via background fetch?

I’ve had no issues opening a local realm in a background fetch, but it seems a flexible synced realm is blocked from being accessed. i.e.

Realm at path '/Users/XXXXXX/Library/Developer/CoreSimulator/Devices/2EBE2645-817B-403D-B4EE-47E78EB4B528/data/Containers/Data/Application/5F9BDEE3-CC08-4D96-8BFA-2EACE9EFE52B/Documents/mongodb-realm/xxxxx-xxxx-jkjzx/6485f1fb856423dcdb19f612/flx_sync_default.realm' already opened with different sync user

In theory, I am opening the realm with the same user and the exact same config. i.e.

  const app = Realm.App.get(appId);
  const realmConfiguration: Realm.Configuration = {
    sync: {
      user: app.currentUser

Anyone else achieved this?