Another thing to consider - how much time between each of the 5 flushes?
In the context of flushing the liver and gall of stones, the liver can be thought of as the stones factory & main warehouse. Like any factory, sometimes the shipping department is able to deplete inventory at the main front docks (close to the bile ducts) quicker than what can be delivered to the docks from the back depths of the warehouse (waaaaaay back inside the liver). Some of Hulda's writings sort of describe this back-to-front progression of stones through the liver. It seems reasonable that it may sometimes take more time (days, weeks, months?, I dunno) for the next delivery of stones to get from the deeper depths of the liver to the front where the ducts are, especially if there was relatively short time between the two flushes that produced lots of stones and the flushes that produced no stones. Perhaps more time is needed in between flushes to give this process a chance to happen. The other possibility is that your clean already, although Hulda seems pretty adament based on her research that the average liver needs to be emptied of 2000 stones before it's condiered fully flushed. Either way, sounds like you are doing really good!