Was the reason Job suffered, as described in the Bible, due to his karmic debt backlog from previous lives, (lives he was not consciously aware of perhaps) and not a spurious bet between Creator and a fallen angelic?

Both are factors here. The karmic debt was the driving force for the problems visited on Job. It was the prior transgressions in causing much harm, both to others and to himself, and this is why the consequences were so severe in nature. Both are major offenses in terms of being at variance with divine alignment. This will always need a correction and a return to the divine path. If this is not done quickly, the consequences of the misalignment will grow. Any harm caused to secondary parties or tertiary parties who are in a widening circle of influence but in harm’s way from wrongdoing, all of their suffering will be added onto the obligations of the perpetrator creating the original insult and injury, and this causes the problem to mount over time. It can be a quite serious compounding of negativity and become quite a liability for someone going forward to even survive the onslaught of negative energy they must contend with, especially if it comes all at once or in quick succession through a series of energetic confrontations, it can be quite a force to reckon with and drags many down to the breaking point. People will succumb to illness and infirmity within the body caused by such negative karma. It can cause a rapid death. It can cause a person to end their own life when the suffering becomes unbearable. Karma is demanding and this is important to know because the perpetrator is putting a noose around their own neck—how tight it will be drawn will be the result of their own actions.