Hello, I think I'm experiencing the same problem here. My Ryzen 5 2400G system freezes often, especially under some high cpu and disk activity, even after the "Typical Current Idle" UEFI workaround. Sometimes I could reboot with sysrq, most of the times I need a hard reset. The freezes never leave a message in kernel log until today, after 2 months I built my machine. 


6月 16 23:29:00 sfc-DESKTOP kernel: [drm] No hardware hang detected. Did some blocks stall?
6月 16 23:29:00 sfc-DESKTOP kernel: [drm:amdgpu_job_timedout [amdgpu]] *ERROR* ring gfx timeout, last signaled seq=1217227, last emitted seq=1217229
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0: VM_L2_PROTECTION_FAULT_STATUS:0x00000000
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0:   at page 0x000000011241a000 from 27
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0: [gfxhub] VMC page fault (src_id:0 ring:24 vmid:1 pasid:32768)
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0: VM_L2_PROTECTION_FAULT_STATUS:0x00000000
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0:   at page 0x0000000112414000 from 27
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0: [gfxhub] VMC page fault (src_id:0 ring:24 vmid:1 pasid:32768)
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0: VM_L2_PROTECTION_FAULT_STATUS:0x00000000
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0:   at page 0x0000000112416000 from 27
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0: [gfxhub] VMC page fault (src_id:0 ring:24 vmid:1 pasid:32768)
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0: VM_L2_PROTECTION_FAULT_STATUS:0x00000000
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0:   at page 0x0000000112410000 from 27
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0: [gfxhub] VMC page fault (src_id:0 ring:24 vmid:1 pasid:32768)
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0: VM_L2_PROTECTION_FAULT_STATUS:0x00000000
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0:   at page 0x0000000112412000 from 27
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0: [gfxhub] VMC page fault (src_id:0 ring:24 vmid:1 pasid:32768)
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0: VM_L2_PROTECTION_FAULT_STATUS:0x00000000
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0:   at page 0x000000011241f000 from 27
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0: [gfxhub] VMC page fault (src_id:0 ring:24 vmid:1 pasid:32768)
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0: VM_L2_PROTECTION_FAULT_STATUS:0x00000000
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0:   at page 0x0000000112425000 from 27
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0: [gfxhub] VMC page fault (src_id:0 ring:24 vmid:1 pasid:32768)
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0: VM_L2_PROTECTION_FAULT_STATUS:0x00000000
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0:   at page 0x0000000112427000 from 27
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0: [gfxhub] VMC page fault (src_id:0 ring:24 vmid:1 pasid:32768)
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0: VM_L2_PROTECTION_FAULT_STATUS:0x00000000
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0:   at page 0x0000000112429000 from 27
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0: [gfxhub] VMC page fault (src_id:0 ring:24 vmid:1 pasid:32768)
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0: VM_L2_PROTECTION_FAULT_STATUS:0x00101031
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0:   at page 0x0000000112421000 from 27
6月 16 23:28:50 sfc-DESKTOP kernel: amdgpu 0000:38:00.0: [gfxhub] VMC page fault (src_id:0 ring:24 vmid:1 pasid:32768)

The HDD led still flashes after this freeze, but in the previous freezes, it won't flash at all.

using kernel 4.17.0-041700-generic on Ubuntu 18.04, mesa 18.1.1-0~b~padoka0. CPU runs at stock 3.6GHz, memory 16G DDR4, running at 2133MHz, no overclocking.