AdMob low interstitial show rate

I have 2 apps with the same interstitial implementation, but in the first I have a show rate nearly to 100% and in the second about 65%. Anyone has the same problem?

My show rate is 62% over 8 apps. So its not that bad.

Yes, but the navigation pattern is the same in both apps, so I don’t understand the different show rate (fill rate is nearly 100% in both apps)… the only difference is in the amount of daily requests: 500k vs 50k… and the worst show rate is in the second case.