The support contacted me, was interested in the problem with the shirt and immediately sent me a new one. Wow - that's super service! And what can I say: the problem no longer occurs with the new shirt.
Thank you Band of Climbers...
The shirt is comfortable to wear and fulfills its purpose: it is light and wicks sweat well. I don't know how durable it is though. After only two uses, it is slightly rubbed in the chest area. Although I only wore it under a light jersey. Conclusion: function top, quality not convincing. 3 Stars!