Tonex App/ iOS crashing/ closing after start

Why throw away the Iphone 6s if it’s still good enough for Amplitube and Tonex. That was the thought. But while Amplitube is working fine, Tonex keeps crashing/ closing again immediately after I start. Access to microphone is granted, so that should not be the reason. I also have Iphone 8, where Tonex is working like a charm. Thanks