I did a couple bathroom tile-over jobs (12 x 12 porcelain) using Mapei Eco Prim Grip for the first time, which is a bonding primer. The existing floors were mosaic, nice and solid.
It turned out fine over all, except that I needed to pop a couple lipped tiles and redo them. They pulled up in whole pieces, applying a heavy, sharp hit with mallet and scraper. My setter had used speedset instead of Ultraflex II, like I wanted. I let it slide, but would make sure to insist on a good modified thinset next time.
As for your floor, sounds like you're on the hook due to poor adhesion/bond. Either wrong thinset, improperly mixed or floors were not clean.