These are the errors that are currently present in my project after I downloaded the beta version of Xcode 9.
This directly connects to this po
From your stack trace, it looks like both calls are Firebase related. As such, try upgrading to the latest Firebase version 4.x to see if those go away.
Please see this question if you may need some help when doing so.
Update. Actually, it looks like this is a known issue in Firebase v4 iOS SDK :-(