Please see my original report and discussion on ROCm:
https://github.com/RadeonOpenCompute/ROCm/issues/605

Basically, the manually configured sclk is reset (lost) on monitor state change
("monitor on").

As per @kentrussell's feedback there, I'm reporting this as a suspected amdgpu
issues related to power management.

I can reproduce with a recent 5.0 kernel and most recent ROCm (2.2).

~$ uname -a
Linux x2 5.0.2-050002-generic #201903131832 SMP Wed Mar 13 22:35:19 UTC 2019
x86_64 x86_64 x86_64 GNU/Linux

apt list --installed | grep rocm

WARNING: apt does not have a stable CLI interface. Use with caution in scripts.

rocm-opencl/Ubuntu 16.04,now 1.2.0-2019030702 amd64 [installed]
~$ apt list --installed | grep hsa 

WARNING: apt does not have a stable CLI interface. Use with caution in scripts.

hsa-ext-rocr-dev/Ubuntu 16.04,now 1.1.9-55-gbac2a9b amd64 [installed,automatic]
hsa-rocr-dev/Ubuntu 16.04,now 1.1.9-55-gbac2a9b amd64 [installed,automatic]
hsakmt-roct-dev/Ubuntu 16.04,now 1.0.9-121-g876627e amd64 [installed,automatic]
hsakmt-roct/Ubuntu 16.04,now 1.0.9-121-g876627e amd64 [installed,automatic]

I have reproduced this bug on a wide range of AMD GPUs. Most recently on AMD
Vega64.