Karndean New Build

Christine24

New build floor was laid in 2 parts leaving a join down the middle. Flooring company saw this join said no problem
Had Karndean fitted and few month later the join is showing through
flooring company lifted tiles and screed has cracked so filled with a resin but joint has come back through again. The are now say the sub floor must me moving Builders are disputing any movement in floor.
Also bumps appearing in flooring
Bathroom also laid with Karndean on top of chipboard but they have not used plywood is this correct, they say the screed they use does not need plywood but am now seeing lines appearing?
Any advice please

UncleZen

This may help:
https://www.karndean.com/en-gb/commercial-flooring/tools-and-resources/resources/flooring-installation/subfloor-preparation