i agree with others that a 10mm seration only is insufficient for bonding a 12mm large format
tile, I never
tile directly to the ribs, always back butter the back of the
tile but with large format always aerate the back of the
tile, this will also help with the concern of levelling clips pulling the
tile from the adhesive bed.
Tiling onto a gypsum screed with a
cement based adhesive is something I don’t do either, I would have used a decoupling matting fixed down with a gypsum based adhesive first then
cement based on top of matting.
Did you take note of the pot life of the adhesive and also the open
tile as this could be something as simple as the adhesive skinning over or still being used from the bucket after recommended pot life.
Never used Norcros before and I can’t seem to download a data sheet on the adhesive you have used to find out pot life and open time ( did you check this before using?....if so did you adhere to these times?
2mm to 10mm bed depth doesn’t give me much
confidence either......I always like to use an adhesive that allows up to 15mm.......ultra SPES is my choice as maximum bed depth is 20mm not that you would bed out that much but just my preference you don’t need to be concerned with bed depth so much when laying large format onto a bad floor.
I think the fact you didn’t do a moisture test on the screed first could be a concern too.
Anyway I hope you get to the bottom of it and rectify the issue so you don’t have this problem again for future installations.