iOS Simulator vs. iPhone

I tried to use your improved Version to rebuild the voicepedia app (https://apps.apple.com/us/app/voicepedia/id1048351656). The Problem is that it doesn't work on the real phone. After the first time I use the tts, it isn't working on the phone anymore. I use singleton so I always use the same instance. Until now I'm not able to fix the issue. Maybe you have an idea.