OP,
You could show any quoting roofer this thread - at least, it will say that you have some knowledge of roofing repairs.
Your Gutter guards are helping but they dont stop sludge accumulating in the gutter or stop foliage growth.
Neither do they remove leaf debris from sitting on top of the guards - which you have front & rear.
The main sewer line might be dropping downhill in all the backyards - blockages often show at the lowest level - thats why its good for you to know where the nearest manhole is.
Your neighbour also has a detached individual step flashing thats sitting on your roof near the front gutter.