For instance, for post A:

In the api, it shows:

{
        "name": "impressions",
        "period": "lifetime",
        "values": [
          {
            "value": 19826
          }
        ],
        "title": "Impressionen",
        "description": "So oft wurde dein Beitrag angezeigt.",
        "id": ".../insights/impressions/lifetime"
      }

However, in Instagram platform, it shows a higher impressions count, which is ~24k.