Regarding your problem, I think it is very difficult to make a remote diagnosis of any problems without the possibility to see the floor live.

I remind you that by law the floors have a one-year warranty on hidden defects, as probably could be defined the defects that you described to me. Therefore, both the reseller and the producer cannot be called to answer, because too much time has passed.

A first choice floor does not mean that its resistance is guaranteed for several years! Wrongly, the customers think that the tiles are all the same, but this is a big mistake. This school of thought has grown in recent years, suggested by DIY chains and misleading commercials - including television - that offer products for a few euros, where the products are actually first choice but the components (enamels and anything else used in producing them) are definitely very cheap. This is made for offering them on the market at a dirt-cheap price, and the limited duration is its tragic consequence.

Even in the floors there is a scale of values, which is not always considered by customers, forgetting that the purchase should have a duration of at least twenty years and remake a job already done triples the costs. 

I have done an example not directly linked with the mentioned situation, because I do not know any details about the purchase and the installed product; but, most of the time, the poor quality of the purchased products is the cause of the problems that arise over time, which unfortunately there is no remedy except the complete renovation of the floor itself.