I have Ryzen 3 3200g and HyperX DDR4 3200MHz dual channel RAM. When i disable XMP, the RAM clock goes to some low value when idle and 1200MHz (max) when stressed.
When I enable XMP, the memory clock is 1600MHz (max) all the time.
It's supposed to be high all the time, RAM doesn't down clock like a CPU and GPU.
The problem can come from the CPU which reduces to avoid overheating, it requires a good cooling of your entire installation. Or manually resume the setting of RAM in the bios.