I am encoutnering a very distincitve but persistent problem with my Ionic4 app on android.
If I run app in debug mode with ionic cordova run android it works without problems (all the same if I add --prod flag here).
But when I create a release build with ionic cordova build android --release --prod, sign, zipalign and install it on my phone, the first launch after install always shows splash screen and white blank screen after that.
If I kill the application, and run it again after that, It works normally … 
Ionic:
ionic (Ionic CLI) : 4.3.1
Ionic Framework : @ionic/angular 4.0.0-beta.15
@angular-devkit/build-angular : 0.8.7
@angular-devkit/schematics : 0.8.7
@angular/cli : 6.2.7
@ionic/angular-toolkit : 1.1.0
Cordova:
cordova (Cordova CLI) : not installed
Cordova Platforms : not available
Cordova Plugins : cordova-plugin-ionic-keyboard 2.1.3, cordova-plugin-ionic-webview 2.2.0, (and 9 other plugins)
System:
Android SDK Tools : 26.1.1 (C:\Users\Uporabnik\AppData\Local\Android\Sdk)
NodeJS : v8.12.0 (C:\Program Files\nodejs\node.exe)
npm : 6.4.1
OS : Windows 10
cordova-plugin-android-permissions 1.0.0 “Permissions”
cordova-plugin-customurlscheme 4.3.0 “Custom URL scheme”
cordova-plugin-device 2.0.2 “Device”
cordova-plugin-ionic-keyboard 2.1.3 “cordova-plugin-ionic-keyboard”
cordova-plugin-ionic-webview 2.2.0 “cordova-plugin-ionic-webview”
cordova-plugin-safariviewcontroller 1.5.4 “SafariViewController”
cordova-plugin-screen-orientation 3.0.1 “Screen Orientation”
cordova-plugin-splashscreen 5.0.2 “Splashscreen”
cordova-plugin-statusbar 2.4.2 “StatusBar”
cordova-plugin-whitelist 1.3.3 “Whitelist”
cordovanetworkmanager 2.6.0 “cordovaNetworkManager”
es6-promise-plugin 4.2.2 “Promise”