<PBXResourcesBuildPhase UUID=..> attempted to initialize an object with an unknown UUID

The reason that happened in my case was some developer updated a pod A while I installed a new pod B (without updated pod A). So when I merged his codes I got the warning.

An easy way to fix this is to

1. remove libPods.a from General->Linked Frameworks and libraries 
2. run `pod install` or `pod update "an-existing-pod"` again. 

For step #2 the purpose is to update .xcodeproj file not to install pod again. If pod is already there cocoapods will just update .xcodeproj file.

Xcode 8 - 11

Target > General > Linked Frameworks and Libraries

Step 1: Deintegrate your project from CocoaPods. Removing all traces of CocoaPods from your Xcode project.

$pod deintegrate ProjectName.XCODEPROJ

Step 2: Install the pod Again

$pod install

Make sure you are replacing ProjectName.XCODEPROJ with your project name.