we have the same setup, here's our solution (for the DTM property in the iFrame)
1) create a data element "in iFrame" which returns "yes" or "no". check by Javascript if the page is loaded in an iFrame. possible code see here: https://tommcfarlin.com/check-if-a-page-is-in-an-iframe/
2) in your page load rule add a new condition like "in iFrame = no"
this setup should stop tracking the pageload within the iFrame.