I am getting the following error in IE 11:
SCRIPT5007: unable to get property \"toString\" of undefined or null reference recaptcha__iw.js (451, 41)
Add this meta on the html header to enable some HTML5 feature for Internet Explorer 11..
If it's not working then open Compability View Settings and remove google.com
Open developer tools and go to Emulation tab then change document mode to Edge..
If it's still not working then add this polyfill on the header..
Actually invisible recaptcha already supported for Android Stock Browser 4.0+ too.. So you don't need to worry if only old browser that doesn't supported..