Above mentioned tests for ram are important and can even help identify which card. You also need to know if you're using a or b type ram slots (I'm assuming you have 4 total so you would typically see A1B1A2B2. Consult your motherboards user manual for exact specifications) because you wont get full power with each one. Also most cpus will throttle the ram frequency if you don't enable the .xmp profile in the bios. This profile is usually from intel and will allow for the ram to run at advertised speed with automatic voltage adjustments that would be needed for stability. I use a 2 ram slot mid range laptop and my bios doesn't support .xmp so I'm capped at 2666mHz but my timespy score is over 7000.
http://www.3dmark.com/spy/8763157
Even with a 2060 RTX laptop gpu I managed to get this score without overclocking by selecting dual band ram cards at 2666mHz with the lowest CL as possible. You're running 3000mHz but even with .xmp enabled your number of clocks per cycle can increase your latency to the point where you're technically not any faster than a lower mHz ram setup. I also undervolted my i7 9750h cpu to prevent thermal throttling and found that my performance actually went up. The only downside to undervolting is if you push to far your system will shut down, but it will not damage the hardware. You just increase the voltage back to where it was and good as new.
I know this might not help your ram issues but hopefully through one of those ram benchmark/stress tests mentioned above you can Identify which module is the problem child and hopefully get your money back.
Also I may note that during stress tests the RAM is usually prone to fail quickly if it is faulty. You probably can identify issues within 30 minutes rather than leaving it running overnight (which can be dangerous because you are no longer monitoring performance or temperature and cannot turn off the test if something looks like its getting overworked.)