ios - FirebaseTableViewDataSource crashes on user signout and signin -

my app has uitableviewcontroller uses firebasetableviewdatasource (from firebaseui). table shows user's bookmarked posts correctly, when log user off, , log user in, app crashes following message:

* terminating app due uncaught exception 'nsinternalinconsistencyexception', reason: 'invalid update: invalid number of rows in section 0. number of rows contained in existing section after update (1) must equal number of rows contained in section before update (2), plus or minus number of rows inserted or deleted section (1 inserted, 0 deleted) , plus or minus number of rows moved or out of section (0 moved in, 0 moved out).'*

i suspect problem related how firebaseui updates content of tableview. i've being debugging past 4 days; searched questions; read relevant docs none mentions unique issue. appreciated.

the details (sorry it's long)

this database structure:

| +-posts |   | |   +-$postid |        | |        +-/* properties of post: title, text, etc */ | +-users    |    +-$userid         |         +-bookmarks              |              +-post1: true              |              +-post2: true 

i using firebaseui show user his/her bookmarks passing users/$userid/bookmarks ref firebasetableviewdatasource query. each key, observe single value event on posts/$postid in order retrieve post details...code below:

self.authstatelistenerhandle = firauth.auth()?.addstatedidchangelistener { auth, user in      guard let user = user else {         return     }      self.query = firdatabase.database().reference().child("users").child(user.uid).child("bookmarks")      self.tableviewdatasource = firebasetableviewdatasource(query: self.query!, view: self.tableview, populatecell: { (tableview, indexpath, snapshot) -> uitableviewcell in          if snapshot.exists() {              let postref = firdatabase.database().reference().child("posts").child(snapshot.key)              let cell = tableview.dequeuereusablecell(withidentifier: bookmarksvc.reuseidentifier, for: indexpath) as! minitablecell              postref.observesingleevent(of: .value, with: { (snapshot) in                 if snapshot.exists() {                     let post = event(snapshot: snapshot)!                     let postvm = eventviewmodel(post: post)                     cell.populatecellwithevent(postvm)                     cell.delegate = self                 }             })              return cell         }         else {             return uitableviewcell()         }     })      self.tableview.datasource = self.tableviewdatasource } 

i put above code in viewdidappear , remove authstatelistenerhandle in viewwilldisappear so

override func viewwilldisappear(_ animated: bool) {     super.viewwilldisappear(animated)     if let handle = self.authstatelistenerhandle {         firauth.auth()?.removestatedidchangelistener(handle)     } } 

almost works fine except, when viewing bookmarks user, log out , log in, app crashes message

* terminating app due uncaught exception 'nsinternalinconsistencyexception', reason: 'invalid update: invalid number of rows in section 0. number of rows contained in existing section after update (1) must equal number of rows contained in section before update (2), plus or minus number of rows inserted or deleted section (1 inserted, 0 deleted) , plus or minus number of rows moved or out of section (0 moved in, 0 moved out).' *

in viewwilldisappear set self.tableviewdatasource = nil. so, don't update datasource improperly.