Steven Zahm@ Karl
The 1x is not the problem. The srcset is a “new” (actually well supported for a while now) standard syntax to support responsive images. IE11 does not support this natively. This support is adde by Connections using the Picturefill polyfill.
If the image URL/s are correct and the images do display when manually typed in the browser address by this indicates that either Picturefill is not being loaded on the page any more or more likely since this just happened. Another plugin or theme update is causing a fatal javascript error on the page, effective breaking all javascript after the error. You can check browser’s console (F12 and click the Console tab) for errors.
You can also try the the theme and plugin conflict tests:
- How do I check for a theme conflict?
- [How do I check for a plugin conflict?](How do I check for a plugin conflict?)
Hope this helps!