Ionic-native 'plugin not installed' but 'ionic plugin add' says already installed

I was frustrated with this issue for a couple hours… in my case, it seems to be an XCode issue.

1. Close XCode
2. ionic cordova build platform iOS
3. re-open XCode
4. Works!

Xcode 9.3

cli packages:

@ionic/cli-utils  : 1.19.2
ionic (Ionic CLI) : 3.20.0

global packages:

cordova (Cordova CLI) : 8.0.0

local packages:

@ionic/app-scripts : 1.3.7
Cordova Platforms  : ios 4.5.4
Ionic Framework    : ionic-angular 3.4.2

System:

ios-deploy : 1.9.2
Node       : v8.4.0
npm        : 5.7.1
OS         : macOS High Sierra
Xcode      : Xcode 9.3 Build version 9E145

Environment Variables:

ANDROID_HOME : not set

Misc:

backend : pro