Issue
DOM manipulation statements in onLoad client scripts fail after listV3 is enabled.
Cause
The listV3 DOM is different from listV2.
Resolution
DOM manipulation is not advised as it causes issues such as these. Read more in the product documentation: Avoid DOM Manipulation.
We can wrap the DOM manipulation commands such as these in addAfterPageLoadedEvent in the onLoad client script as below.
function onLoad() { addAfterPageLoadedEvent(function(){ document.getElementById('lookup.incident.u_business_service').style.display = "none"; }); //Your rest of the onload script }