When you run a CPC based push notifications campaign, please pay attention that you may get some late/reaching clicks.
In order to prevent traffic overflow, we have implemented an internal algorithm in order to avoid that. 

Here is how it works in brief: 

After you've started the campaign, we serve a certain number of impressions, calculated according to the daily budget and bid settings.
After that the campaign pauses and system awaits for the reaching clicks to come, that's when you see the message "Paused: out of daily impression limit (this status usually takes a few hours).
Then the campaign can start again and get another portion of impressions and pause again to consider the new information about the number of late clicks and change in CTR.

Thus, campaign stops every time when it reaches the calculated amount of impressions limit and resumes later to finally hit the limits you have set for it originally. 

You can also increase daily budget in order to restart the campaign.

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