iFrame scrolls to top upon click on some items on iOS

I have made a video of the issue: https://drive.google.com/open?id=10AhL2KUZpQJpsnkjuP_3y46mu3lQ0dTZ

You can see that the scrolling is working fine. And I can also use other buttons and fields just fine. The issue is only on iOS (both in the simulator and on a test device), but not on Android or in the browser.

I'm using ionic 4 with angular and cordova. The code is as follows:

<ion-content>
  <div id="shop-wrapper">
    <iframe scrolling="yes" id="shop" src="http://shop2.boettcher.ch/de/schnelleingabe.htm"></iframe>
  </div>
</ion-content>

And the css

#shop-wrapper{
  -webkit-overflow-scrolling: touch !important;
  overflow-y: scroll !important;
  height: 100%;
  width: 100%;
}
#shop-wrapper iframe{
  height: 100%;
  width: 100%;
}

I gave you the proper url so that you can check that there is nothing unusual on the buttons.

I have been on this for days and desperately need some help.

from iFrame scrolls to top upon click on some items on iOS