I assembled two 12V batteries from the 8 cells that I purchased from Amy. One of the batteries has performed very well, with all of the cells staying within a few mV of each other. The second battery also performed very well until the very end of the summer when one of the cells refused to balance. I used a Victron Smart Shunt to track SOC which agreed with the SOC's provided by the BMS's so I was fairly confident that the batteries were providing the expected capacity. I don't have a ZKE-40 so the best I could do was disassemble the problem battery, top balance the cells and then monitor their respective individual voltages. As I expected, the problem cell voltage quickly diverged from the other three. I assume that the cell has developed some type of internal soft short that has increased its self discharge rate. That is pure speculation on my part though. I have done my best to baby the cells, both physically and electrically, from the moment they arrived at my house. But there is no way of knowing if I somehow inadvertently caused the cell problem or if the cell has a defect that only showed up after 5 months of daily cycles.280K v1/v2 has a slew of issues but it could also be you have not assembled properly. Only way to test would be on a device like a ZKE-40 and perform a full charge / discharge test and see if you see any funniness with the curves.
Luyuan is doing whatever they can, they are selling good cells with test reports, but at the end of the day its hard to know if its a user problem or an item problem.
I can bet many user errors lead to false conclusions of cell quality.