An asynchronously loaded script is likely going to run AFTER the document has been fully parsed and closed.
Thus, you can't use document.write() from such a script (well technically you can, but it won't do what you want).

You will need to replace any document.write() statements in that script with 
explicit DOM manipulations by creating the DOM elements and then inserting 
them into a particular parent with 
.appendChild() or 
.insertBefore() or setting 
.innerHTML or 
some mechanism for direct DOM manipulation like that.