After Updating my Nuget Package for Forms 188.8.131.52 I have found that the validators for custom form elements are no longer rendering in the cms in Internet Explorer, However they render just fine in Chrome. IE version: 11.0.960.18282. Our client mainly uses IE so I downgraded back to Forms 184.108.40.20600.
This is a bug (using unsupported function in IE). We're fixing in upcoming release. Thank you.