NRF91 at client sample

Hi , 

Using the at client sample, i get this print :

***** Booting Zephyr OS v1.13.99-ncs1-5904-g71a875c18e2d *****

The AT host sample started

but I cant send any command (no response).

the weird thing is, that I can send commands via asset tracker.

Any idea why ?  

already tried erasing flash / resetting