I somehow got the logs working (the corresponding flags under "Diagnostics" were already checked in my case), however, I do not always see my logs. Every now and then I need to re-deploy the app (without modifying any code) in order to see the logs.

Thanks to the now functional logs and your hint regarding ECMAScript 2015, I managed to get the PbxAdminApi working , though this also occasionally demands re-deployment in order to work.

I will keep an eye of things and come back here in case the issue persists. If you have any idea what the cause might be that it only occasionally works, I'd be grateful if you could tell me.