Tiles cracking on new shower nib wall - Tile Advice

[Janie]

Hi, We have recently had our bathroom updated and a new Brick nib wall put in and tiled. Within 6 weeks it had cracked on both sides and metal trim had come away. The bathroom renovator came back and replaced the tiles with new adhesive (type used in pools) but I have noticed after 3 weeks it has cracked again and started coming away from trim. Can you advise if this is an adhesive issue or a brick wall issue or something else. Photos attached. Thanks.

 

[Dave]

Looks like stress cracking, what substrate is it. ?

 

[Janie]

Looks like stress cracking, what substrate is it. ?

Sorry what is substrate?

 

[Dave]

Sorry what is substrate?

The background the tiles are fixed too.

 

[Janie]

The background the tiles are fixed too.

It is a brick wall, single layer that was built in front of existing brick wall. Floor is concrete. Some of the concrete floor was dug up to put in new drain in shower and replaced with concrete. Drain is very close if not very slightly under the shelf wall (less than1cm)