HTML Alert – Exception: Cannot retrieve the next object: iterator has reached the end

I’m trying to call this upload script in an html alert in the spreadsheet:
drive-multi-upload

For that I’m using this function in the Code.gs file:

function showDialog(){                                              
const TEMPLATE = HtmlService.createTemplateFromFile('forms'); // calls the html page where the alert template will be
    
const HTML = TEMPLATE.evaluate().setWidth(600).setHeight(400); // we prepare the template to be loaded

SpreadsheetApp.getUi().showModalDialog(HTML, " "); // we load the template on the screen
}

The issue is that if another account clicks the button to upload the file, the message Exception: Unable to retrieve the next object: the iterator has reached the limit. is displayed.

How can I resolve this?