RAM speed fluctuating big time. Is this normal?

I've tested both slots and different sticks and both show the same result in HWINFO64, that the RAM is going back and forth/fluctuating between 1064Mhz and 665Mhz. CPU-Z also shows latency changing respectively between 15-15-15-35 and 10-10-10-28. Is this at all normal? The notebook is Dell Latitude 7460.

Thanks for any answers. Just received this notebook secondhand and it's perfect other than this. I don't want to cause any issue with the seller if this isn't something to worry about in regards to a hardware problem.

Any ideas? Thanks much!