Application two ways on solid walls or construction wooden cladding metal cladding or brick wall. Size of kerdi board is not very wild just 60 cm.
Applying in to stud wall 12mm board is the beginning of the problem.
First thing first board is not solid on the wall when joist from joist in cladding is bit wilder than should be this affecting strength of kerdi.
Tile simply give away when trying to press to kerdi board even when tile adhesive is bit more dissolve to create less impact on board.
More you press more force coming back.