Airpods cut out when iphone is in my front pocket

My Airpods work like a charm when I have my phone in my hand or on the desk, however, when I put my Iphone (6s, latest IOS) in the front pocket of my jeans, they constantly cut out when listening to Spotify (Downloaded content).

Even if I put the phone in my back pocket, the issue almost goes entirely away. However, in my front pocket, they are close to unusable, especially while walking. This seems so weird and I am at a loss. (I have no keys or similar in my pocket).

Has anyone experienced anything like this? I have reset them already to no effect. Really don't know what to do next here. Is that a hardware flaw that I should have looked at?

Any advice is much appreciated.