Change in Adword campaign performance

I'm running several adword campaigns for app install, it was working fine, but due to limitation of finance, I had to decrease budget and later on decrease the bid

After few days, I got enough money so I "Undo" all changes, the budget increased and worked fine
but surprisingly the number of installs dropped significantly?

so with the same traffic but I receive lower installations

What analysis I have to do or check to see where is the problem?