IOS 12.1.4 - Apps bugged, can't delete or reinstall
Managed to fix it with 'Apple configurator 2' (https://itunes.apple.com/us/app/apple-configurator-2/id1037126344?mt=12). Connect iphone to macbook, launch Apple configurator 2, select device, click 'add -> apps', login with apple id, find spotify, click 'install', choose 'overwrite existing'. 

Now on iPhone go back to the app-store and you can redownload it.