Feedmeink already said most of it but I'll just add that HCI Memtest doesn't require you to purchase the pro version and has a free version. The Pro version isn't expensive though. That is the easiest way to test individual sticks: put one in, run memtest
Regarding your stability, sometimes you might find 4 sticks unstable on the same settings but all test fine individually. This could be an indication you are asking too much of the integrated memory controller on the CPU. You either need to clock the memory lower, loosen timings, or increase memory controller voltages (BE CAREFUL)
I agree that's annoying. 😞 I'm not going to violate their license though. Hopefully they get back to you.