Different revisions of the same RAM will have different xmp profiles.  So for example if you buy kingston hyper x fury in 2017, and then another stick in 2020, it will likely contain different timings on the xmp profiles.  For example, there was an update to hyper x fury timings on retail hyper x fury ram at the end of 2019.  Also, retail hyper x from amazon ALWAYS has different timings than Dell oem hyper x fury ram.  If the ram has different xmp profiles, they cannot be run with xmp enabled, because only one profile can run at a time.  This is different from being matched, as you can often run mismatched ram it will default to the slowest common denominator if possible.
Hello, i bought an aurora r6 some time ago with a single module 16gb 3200 mhz  ram. I bought what i believed to be the same ram to upgrade it to 32gb but for some reason xmp is disabled in the bios and ram is only running at 2400mhz even though both are 3200mhz xmp compatible from the same brand. im so lost. i tried different dimms but same result. i also tried them both independently and they are indeed both 3200mhz 16gb single module sticks.
Aurora R6, 32GB ram problems!