Half my RAM disappeared?

I'm on an Asus ROG Zephyrus M15 - it has a mobile 3070 TI and an Intel i9-12900H CPU. Up until this week, it had 16 GB of ram, but all of a sudden 8GB of my RAM has just seemingly vanished. In system settings, activity monitor, in the BIOS, and in CPU-Z, along with Amory Crate, it's saying I only have 7.7 GB of usable ram, 8GB in total.

What could be causing this? Did a RAM stick fail? Is there some other issue? I've tried rebooting a few times and nothing seems to help.

Thanks in advance!