The bathroom floor needs to be re-tiled. Most of the mineral tile adhesive has been removed. The floor has been intensively sanded for some time by a non-professional using a repair router.
Judging by the photo, is the floor sufficiently prepared?
The problem with remote diagnostics is always that even the experts among us can't make a definitive decision as to whether or not they were sufficient.
In the penultimate photo on the right, you can see that the reference grain was exposed there during grinding. It couldn't have been better!
But the other photos show light-colored adhesions that are impossible to appreciate.
To illustrate the problem:
If the light-colored areas are deposits of fine sediment (which are found in new screeds, but only as an example), that layer may not have had the adhesion and elasticity to provide a bond between the screed and subsequent layers.
I'm not trying to scare you or "evade" the truth.
If I had seen these surfaces myself, I could immediately, after a cursory inspection, give an appropriate assessment.
If a tiler is going to install ceramic tile, it is their responsibility to inspect the substrate. It is the duty of inspection and due diligence of every parquet installer and tiler.
If the subsequent contractor approves this surface after testing, then we assume it is technically correct.
Otherwise, he (but it is in any case) is liable under warranty for consequential damages that result from his area of responsibility.