Unable to open modal or panel when deployed as a webpart in Sharepoint online 2013 Modern view page

zainkhan - the answer comes very late, but the issue you describe frustrated me over the last days, and I hope I can spare someone the grief. 

The problem you actually have, is caused by the fact you are running the webparts in domain isolation mode - hence the whole IFRAME stuff. 

Disabling this is as simple as going to: /config/package-solution.json and modifying isDomainIsolated to false. 

The tricky part - and what made me climb all the office walls here - was that even after changing the property, repacking and redeploying the solution to the app catalog - I was still getting the iframes. 

Turns out (yeah, i know - i am stupid, took me one day to notice this) you need to fully remove the solution and redeploy it to the app catalog. Only then will it stop running in domain isolated mode.