Weren't there a bowel prep done before (food fasting, plenty of water and laxative consumption) the colonoscopy? Unless it was an emergency/urgent scope under general anaesthesia, the scope detection of stool does seem a bit odd.

Also, the new bleeding may be that your father is not modifying dietary habits (water & fibre) or compliant with taking stool softeners.

did at any point any doctor ever mention "diverticular bleeding"? a single diverticulum missed on scope can be just as frustrating (but not necessarily dangerous) in diagnosing a bleeder. some more compliance to stool softening habits may be needed.