GPU Clock Sudden Drop

[SSK-99]

Hi everyone, recently finished my first PC build. Was playing some GTA today, turned VSync off to check what FPS I was getting and after a few seconds, my VRAM clock droppped from 7000 MHz to either 100 or 400 MHz (I didn't get a good look at it), causing my FPS to drop to sub 10 (from about 100) for about 10 seconds.

 

The 7001 MHz dropped, and one of the GPU usage figures shows 0%:

 

This is what shows in MSI Afterburner if it helps (I have not overclocked anything):

 

Specs:

R5 3600

GTX 1660 Super

16GB 3200MHz RAM

 

I have been running with VSync on and it has been perfectly smooth.

Any idea what that 0% usage figure represents? Is this normal or something I should worry about?

 

Any help appreciated!