I found there is a bug or a glitch in the basic ads system.
Before my account was changed to "On Hold" due to a credit card issue, my app got over 10 installs in average per day.
Now, the credit card issue is fixed and my ads account is restored back to "Active" state. However, even I increased the CPI, I still got ZERO install in the past two days, I think there must be something wrong with my ads account, so my ads is still "on hold". I tried to search many relevant keywords in the USA app store many many times, but I couldn't see my ads being shown.
There must be a bug or a glitch in the system, anyone saw a similar issue before?