Question RAM label says 1333mhz but cpu-z says 1600

[Absolute.Red]

Got this 1333mhz ram from symmtronix (CPU-Z says its crucial )for an old PC. on the lalbel it clearly says 1300mhz PC10600
but CPU-z says its 1600mhz PC12800
i also have a G skill 1333mhz stick.
My issue is, when i run memtest with just either stick connected, everything is fine. (also even when changing slots)
but when i put them together i get some errors in memtest.
What could be the issue?
G skill is like 11+ years old.

CPUZ screenshots:

https://imgur.com/a/7INyhGL

View: https://imgur.com/a/7INyhGL

 

[Lutfij]

They are different sticks of ram, they shouldn't be paired together, which is why you're getting instability/errors. You could still try and see if your motherboard has any BIOS updates pending.

When upgrading your ram, you're advised to invest in an identical stick of ram(at the very least) as you're currently working with or a ram kit.

 

[SkyNetRising]

What could be the issue?

What are full specs of your system?

The problem is - you're combining two different ram modules (different manufacturer, different specs, not from same kit) and
running into compatibility problems.