The reason is still due to irregular construction.
Waterproofing is done, but if there is no standard closed water test and inspection, water leakage will eventually occur.
The national standard for closed water testing requires that it be done twice, once after the waterproof coating is completed and the waterproof coating film has dried; the second time after the waterproof protective cushion or facing layer is completed. Proceed afterwards.
If only the first closed water test is done, the waterproofing may be damaged during the subsequent process of making protective cushions or laying wall and floor tiles.