adMob RPM Drops from 0.24 to 0.13 is it normal?

The last week my adMob RPM dropped to 0.13 after being stable between 0.23 - 0.27

does anyone knows why would this happen , is it permanent or how to recover?


I think the reason is somehow obvious, you have less CTR.

And it can happen because you decreased the refresh rate, or just can happen without any reason