Your floor tile failure was caused by the following factors.
Individually they could have caused failure, but combined it was a certainty.
Chipboard floor - can be tiled onto but only with very special adhesives and with 100% coverage to tile and floor.
Heated floor - can be tiled easily enough but must have an uncoupling membrane such as Schluter Ditra, to separate the adhesive bed and tiles from the expansion/contraction stresses caused by the heating - as seen readily in the adhesive cracks in your photos.
PVA - simply put, this forms a skin and prevents (not aids) adhesion.
Acrylic primers, or SBR only should be used.
C2 adhesive has polymer added to bond to porcelain (standard sand and cement won't bond) but does not have anywhere near enough polymer to increase the flexibility required for a heated, timber floor.
Timber Floor - if your floor is "floating" as I suspect it is, then 90% of professional tilers will just walk away from them. There is just too much risk of movement, both deflection (bounce) and lateral (sideways) movement. They can be tiled. but not without a lot of prep, careful checking and special materials.
Tiles aren't back-buttered. - It is recommended that large format tiles, particularly with waffle backs, are back-buttered with a thin layer of adhesive to aid "bedding in" and ensuring a solid, even bond. It also removes any risk from tiles with dusty backs.
Hope that helps explain what has gone wrong!
