Mixing ECC and non-ECC RAM is a bad gamble.

Probably yes, but the odds aren’t in your favor. Many boards will boot and just disable ECC entirely, treating both sticks as plain DDR. But “not recommended” in the manual usually means the memory controller wasn’t validated for that mix—so you might get random crashes, weird boot loops, or a system that only works with one stick installed.

If ECC is important to you, use all ECC sticks. If it’s not, just buy regular RAM and skip the headache. Mixing almost never saves money or improves reliability—it just adds a variable you don’t need.

You’re better off with a clean configuration.