It's been said that when an organization becomes too large and inefficient, the proverbial left arm doesn't know what the right arm is doing. Two different factions within the same organization unwittingly start working against each other - even as both factions believe they're doing what's in the best interests of the organization overall.
I wonder if this is what happened with the Mongols' flunkies in HSDS.
Consider this: Chan Yau Leung was helping Sing Kwun to take control of the Beggar's Union. Sing Kwun was working under the auspices of the Yuan Dynasty government. And yet, on the occassion when Chan Yau Leung introduced Sung Ching Sheu to the phony Chief See For Lung, Chiu Mun came with the Yeun Ming Elders to interfere with Chan's plans. The Yeun Ming Elders and Chan Yau Leung must have wondered what they were doing fighting each other and getting in each other's way. Both were in the employ of Chiu Mun's father (Mongol warlord Toghon Temur). Did they ever question why they were attacking their own allies?