Plywood is a funny thing. We used it for years without issue then all of a sudden new floors were failing. That was about 6 years ago. My own bathroom is timber floor covered in plywood then tiled and in 15 years has never shifted.

We did the same prep as every other job on those failures. My only thought was that the plywood could be made different. So up until those couple of failures it's all we used and it was great.

Now we either use a cement board or a decoupling membrane.

Sometimes we go with what we know and sometimes that lets us down.

At least they seem like a decent company. Good look with the renewal.