IOS 10.3.1 Chrome browser CORS fail
Specifically regarding the iframe issue, it appears that this error is related to Chrome autofill. You can reproduce the error using the sample code provided in comment 6 of the associated chromium issue (worth reading all the way through):
<body> <iframe src="http://example.com"> </iframe> <script> window.addEventListener("error", function (e) { alert("Error occured: " + e.error.message); return false; }); </script></body>If you open this page in iOS Chrome, it will pop an alert with the above error. If you go to Chrome Settings, turn autofill off, and reload the page, the error is gone. This is tested with iOS 10.3.1 and Chrome version 58.0.3029.113.
There does not appear to be a solution at this time, but it appears that the content in the iframe does load successfully even with the error. As such, there should be no discernable impact on the end user.