It is possible that the firmware on it is corrupt and you need to update the firmware.
One option is from iCUE software but that doesn't help when you already have the latest firmware.
2nd option is manual, that i, once, went through with the help of Corsair support.
Here, i'm not feeling comfortable telling how to do it manually, since it may worsen the things and i only have Strafe RGB firmware file. Strafe should have different firmware file, which only Corsair has.
I suggest that you contact Corsair.

And while you can't replace the KB, since your KB doesn't have any warranty, perhaps Corsair support can help you fixing your KB. They know a lot more about Strafe KB than i do, since they made it.
Few closing words regarding refurbished hardware;
Refurbished hardware is often cheaper than brand new hardware but there's a catch. Often, there isn't any warranty with them, or very little (14 days to 90 days) and with cheap price, you'll be taking a risk. Risk of it either working flawlessly and you got a great deal. Or risk of it not working and you wasting your money.
I, personally, am willing to pay full price (brand new item) with a guarantee of it working and if something should happen with it, i have a guarantee that during the warranty period (min 2 years), i can get it fixed/replaced cost free. I've already replaced my Corsair Sabre RGB mouse under warranty since 1.5 years into service, the middle mouse button stopped working.
Though, there are people out there who are willing to take the risk of refurbished hardware, just to score a great deal. There's nothing wrong with that, but keep in mind the risk you're getting with refurbished hardware.