HP Pavillion Gaming ec-1036ax - CPU drops to 0.39GHz when Gaming on battery / Unplugging

[GaryKhor]

Hi, I am facing a problem that the CPU frequency of the HP laptop will drop to 0.39GHz and cause a serious lag to the laptop.
Condition:

1. Slightly heavy games (including Minecraft) 

When gaming, the CPU will occasionally (quite often sometimes) drops to 0.39GHz and cause noticeably serious lags for few seconds

2. Unplugging charger

When unplugging the charger, the CPU frequency will drop to 0.39GHz and cause lag for all application even though I have no application open (Noticed by task manager and clicking things during that time)

Things Checked:

1. Heat is normal; 60 - 70 Celsius

2. Power left; Occurs when battery almost full, almost empty, moderate
3. Game requirements; The game is able to run normally when the issue not occur
4. Drivers; Updated Firmware in Device Manager, Uninstalled and Reinstalled both Graphics Card Driver, Updated Windows updates, BIOS is updated

5. Power Plan; Checked Minimum and Maximum CPU to 100%, Reset to HP default power plan
6. Windows Version; Updated Windows from 1909 to 20H2 (Suggested by a HP technical support)

Is there anything else can I do? This issue starts to occur about 1-2 months ago, this is a quite new laptop bought on about August-September 2020.

Or will it be hardware problems?

Any suggestion is appreciated, searched online and found many results but nothing works for now