Appending to an array in Firebase - Asynchronous and reloadData() - ios

Question

I am having trouble with the asychronous nature of Firebase, particulary appending to an array from within an observe function.
Any suggestions or help would be much appreciated :)
The comp that is appended to the users array in the selectUsersComp function disappears when the firebase observe function is exited, even though I reload the data in the collectionView.
I have tried using Dispatch.main.async but it has not helped. I have a Firebase observe function inside another Firebase observe function. Does this change things?
fileprivate func fetchStartedComps() {
let ref = Database.database().reference().child("startedComps")
ref.queryOrdered(byChild: "creationDate").observe(.value, with: {
(snapshot) in
guard let dictionaries = snapshot.value as? [String : Any] else { return }
dictionaries.forEach({ (key, value) in
guard let compDictionary = value as? [String: Any] else { return }
let comp = StartedComp(Id: key, dictionary: compDictionary)
self.selectUsersComp(comp: comp)
})
self.filteredStartedComps = self.startedComps
self.collectionView?.reloadData()
}) { (err) in
print("Failed to fetch comps for search", err)
}
}
func selectUsersComp(comp: StartedComp) {
guard let userId = Auth.auth().currentUser?.uid else { return }
let ref = Database.database().reference().child("startedComps").child(comp.title).child("invitedUsers")
ref.observe(.value, with: { (snapshot) in
guard let dictionaries = snapshot.value as? [String : Any] else { return }
dictionaries.forEach({ (key, value) in
if key == userId {
self.startedComps.append(comp)
}
})
self.collectionView?.reloadData()
}) { (err) in
print(err)
}
}