My rock5b is not able to operate with the memory at full speed (hard lockups, reboots). In order to run a stable system I must underclock the memory using echo 1560000000 | sudo tee /sys/class/devfreq/dmc/max_freq
Unless someone can tell me how to run the memory at full speed, I must conclude that the device is faulty and needs to be replaced.
Have You checked different power adapters?
You may be just missing power and just find some way to use less of it
same issues with nvme and poor chargers, just an idea what can cause those