Did you check ata & brace?

sometimes the string or cable will start to go south UNDER the serving and when that happens its heck to keep a bow in tune until all of a sudden, it lets loose. I had that happen with a bow of mine a few years back that went form a rock steady in tune bow to needing tweaks every few days. I opened the bow case one day and the limbs were nearly straight out, the cable had let go and the bow was only being held together by the string.