hi, i have a 11 month rottweiler bitch. We had a similar problem with her. I had never managed to stop her weeing the house at night but she never pooed, then at 9 months she started pooing every night. Like you nothing had changed at home and i couldnt explain it. After a couple of weeks she started chewing on the door frames and then chewed up the lino in the kitchen. I even tried getting up through the night and letting her out but she still did it. This was completely out of character.
One night i accidently fell asleep with her in the bedroom and when i woke in the morning i noticed she hadnt had any tpe of accident. She has stayed in my room ever since, sleeping in her own bed in the corner of the room.
Ideally i would like to move her back downstairs at some point but for now i am just glad that shes stopped messing in the house. I realise this doesnt suit everyone but its worth ago if your at your wits end, like i was. I know how frustrating it can be.
Good Luck!!!