I also had this problem turns out it was not put on default. so what I did to fix it: navigate to cow overview or health dashboards -> look for customize columns or add data points option -> add n=milk temperature manually -> check sync settings (make sure you are logged in into the same horizon account on both mobile and PC) -> sensor activation check (settings -> devices -> milking robot status) -> and then confirm that milk temp sensors are active. Im not sure if you are having the same problem, so I cant say if this will help you 100%, but just speaking from exxperience

I also had this problem turns out it was not put on default. so what I did to fix it: navigate to cow overview or health dashboards -> look for customize columns or add data points option -> add n=milk temperature manually -> check sync settings (make sure you are logged in into the same horizon account on both mobile and PC) -> sensor activation check (settings -> devices -> milking robot status) -> and then confirm that milk temp sensors are active. Im not sure if you are having the same problem, so I cant say if this will help you 100%, but just speaking from exxperience