This is not a professional answer but I just wanted to tell you that I had a little shih-tzu "dog" that started going right in the floor, right in front of me, when she got older, after being trained for years. I finally turned her into an out door dog.
she lived many more years. she lived to be over 17 years old.
she never did it till she got older. When I started keeping her out doors she would many times not even bother going out in the grass to do her business. she would go right there on the patio. you do not need to pay me for that answer because I am not a vet and it might be something entirely different.
Deann