SharePoint 2016 custom forms not rendering sharepoint:formfields when migrated to sharepoint 2019

I am having an issues with Custom New/Edit and Display Forms in SharePoint 2019 on Prem classic experience (not using PowerApps nor is it currently an option)  the form controls are not rendering on the page.  The title and Description Controls are rendering fine but the input controls are blank and in the DOM are appearing as <span id="WPQ19103594b-6607-4669-9971-e170bd299ed9PhoneNumber" data-sp-options='{"mode":3,"source":"PhoneNumber"}' data-sp-control="SPFieldText"></span>

instead of the correct markup.

Has anyone come across this in 2019 and if so does anyone know what might be causing it?