The floor of the bathroom of the newly bought building was waterproofed, and the top was dusted, but

This is not possible, cracking and some more troublesome waterproof layer cracking, need to be treated before paving the floor tiles.

It should be the problem of the cement mortar screed, for example, the shell - cracks may lead to the shelling. In addition, if the waterproof material is oily and not cement-based waterproofing material, then the cement mortar and the waterproof layer will not have good adhesion performance, so it is easy to produce shelling.

Therefore, you need to understand the nature of the waterproofing material, if it is not a cement-based waterproof material, then if you directly stick the floor tiles on it, there will also be a problem of shelling.

Since I didn't see the scene map, I can only give you some answers based on your description. First of all, after the waterproofing is done, there are still small cracks in the waterproof layer, which is an abnormal situation, indicating that in the process of construction, there may be problems such as insufficient wetness of the base surface sprinkling, insufficient thickness of the waterproof material, and then there is a feeling of movement when stepping on it, which is even more serious. After you do it, do the closed water test!

Cracks may be caused by the cement mix not being blended well or drying too quickly. Generally, it does not affect the waterproofing, but I don't know if you have done a closed water test after your home waterproofing is done, and the shower area of the bathroom must do a 24-hour closed water test.

If the closed water test does not seep water, you can lay floor tiles on it.