Can you clone the widget in global scope and check if the issue still persists?
Also,
There is another way to hide attachments from Service Portal using DOM manipulation but it is not best practice to use DOM manipulation. You can try below code in OnLoad Client script
Table - sc_request
UI Type - Mobile/Service Portal
Type - onLoad
Isolate Script - Set it to false/Uncheck
function onLoad() {
var attachmentButton = top.document.getElementsByTagName('sp-attachment-button');
attachmentButton[0].parentNode.hidden = true;
top.document.getElementsByClassName('sp-attachment-manager')[0].style.display = 'none';
}
If you are doing it through client script, you don't need to clone any widget
