Delivery API does not respond with items

Since one week Delivery API did not respond with product recommendations. Previously it worked. 

What is done:

- product info is send from product pages, 

- hosts are enabled, 

- back-up recommendations are enabled. I tried with multiple ones like: last seen, bestsellers etc Nothing work. 

Recommendations which are put on the www using activities work ...........

Do you have any ideas how to resolve?