Hum, strange indeed! I would suggest the following:

1- Set the scheduler to restart your pc at the desired time you wish to mine (https://v2cloud.com/tutorials/how-to-configure-windows-to-reboot-automatically-on-schedule)

2-Set your PhoenixMiner.exe file to run as an administrator (Properties > Compatibility > Settings - Run this program as an administrator)

3- Create a shortcut of your start_miner batch file and cut it

4- press the windows logo, type run, enter (to open the run app), then type shell:startup and paste your batch file shortcut there (C:\Users\YOURUSERNAME\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup).

Now everytime your pc restarts it's going to start your miner, with the minor inconvenience of you having to manually close the miner when you do not wish to mine...

See if that helps with your hashrate issue. I use the startup thing on my pc and haven't had any issues so far.

Try running PhoenixMiner as an administrator. Hope it helps!

[edit]

The Readme.txt doesn't specifically mention the need for the -powlim command to be run as an administrator, but it's worth a shot.

From the Readme.txt file:

Hardware control options
************************

Here are some important notes about the hardware control options:

* Most recent Nvidia drivers require running as administrator (or as
  root under Linux) to allow hardware control, so you must run
  PhoenixMiner as administrator for the VRAM timing options to work.

* The AMD memory timing options ("-rxboost", "-vmr", "-straps"),
  with the notable exception of "-mt", also require running as
  administrator (or as root under Linux)

That's weird...

I haven't BIOS moded my card, so I would suggest a clean install of your OS (win10? That's what I'm using) along with changing to the default BIOS on your GPU. I'm on 21.4.1 aswell.

Pcie 2.0 has half the bandwidth of the 3.0, so I'm not sure this would be the reason for getting less than half the hash rate of what I'm getting with a weaker card without BIOS mod.

Worst case scenario, try to get a used MOBO with pcie 3.0 if you plan on mining for the future, my rampage 3 extreme is going for around usd 200 on ebay in the US and you could in theory use it with more than 4 gpus without much hassle (i only have one).

Hi, Jameous! Did you check if your GPU is in Compute mode in AMD Radeon Software instead of Graphics mode? (settings > Graphics > Advanced > GPU workload > compute) I've got an RX 570 and I'm getting about 30 MH/s. I'm using the following commands in the start_miner.bat file for the Binance pool:


REM
REM Example bat file for starting PhoenixMiner.exe to mine ETH
REM

setx GPU_FORCE_64BIT_PTR 0
setx GPU_MAX_HEAP_SIZE 100
setx GPU_USE_SYNC_OBJECTS 1
setx GPU_MAX_ALLOC_PERCENT 100
setx GPU_SINGLE_ALLOC_PERCENT 100

REM IMPORTANT: Replace the ETH address with your own ETH wallet address in the -wal option (Rig001 is the name of the rig)

:START

PhoenixMiner.exe -pool stratum+tcp://ethash.poolbinance.com:1800 -wal *YOUR WALLET* -worker *YOUR WORKER NAME* -pass 123456 -tt 55 -fanmin 50 -cclock 1150 -cvddc 900 -mclock 2000 -mvddc 900 -mt 1 -rxboost 60 -logdir (DIRECTORY OF YOUR CHOICE TO STORE LOGS)

REM pause

timeout 5

goto START



You can also use the  " -acm " command to enable compute mode, as shown in the Readme.txt from PhoenixMiner file:

-acm
   Turn on AMD compute mode on the supported GPUs. This is equivalent
   of pressing "y" in the miner console.


Remember to check your specs for the following commands, since they are for overclock and undervoltage configurations of the GPU:

-tt
-fanmin
-cclock
-cvddc
-mclock
-mvddc-mt
-rxboost

Hope this helps,

Falcão

[edit]

By the way, my setup is pretty old :

Asus Rampage 3 Extreme (over 12 years old)

i7 965 OC to 3.6 MHz

6 GB of DDR3 RAM @1333 MHz

[edit 2]

Just did a little research on your MOBO and it is as old as mine, same cpu socket (LGA 1366) and chipset (X 58), so I'd guess your issues are in fact related to your GPU's settings