Admob ad page views much higher than impressions on tablets

I have recently published an app to the Play Store with Admob ads. I noticed something odd today as my page views reported by AdSense were much higher than my impressions (7400 page views vs 1500 impressions). My match rate is still high (90%+) which suggests to me the ad requests are being fulfilled but the ads are not being displayed to the user. I then checked the platform information on AdSense to find that nearly all page views on 'high-end mobile devices' lead to an impression (1800 page views to 1500 impressions) whereas on 'tablets' I have 5600 page views to 13 impressions. This suggests to me that the ads are being displayed fine on mobile phones but barely at all on tablets.

What could be causing this? Are there any additional steps that must be taken to ensure AdMob ads are displayed on tablets as well?

Note: most of my ads appear as interstitials and some banner ads.

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