I have multiple CEF Browsers in my project (approx. 10). They all are added to the viewport. Engine provides SWebBrowser to use CEF. I wrapped it with UWidget by making a class called UBrowserWidget(Although I noticed there is already a UWidget version in form of plugin, so that can also be used.)
So After Creating them and loading any URL in them, When I hide them and make them visible again they become unresponisve to any input, Even Minimizing and then restoring back make them unresponsive. They start working normally as soon as I resize the viewport window.