Async causing "Some files on the server to be missing or incorrect"

[davpai]

I'm trying to optimize the page load time of my site via Google's Page Insight tool.

https://developers.google.com/speed/pagespeed/insights/

Their main suggestion is to remove render-blocking scripts (scripts that require download and being run before page load):

https://developers.google.com/speed/docs/insights/BlockingJS

The suggestion to remedy the render-blocking scripts is to make the scripts asynchronous. However, when I add the attribute "async" to the <script> tags which are being called out (external ones for mailing lists and if someone leaves the page), then the page loads with "Some files on the server may be missing or incorrect. Clear browser cache and try again. If the problem persists please contact website author."

Why is adding async to custom added scripts generating this Muse page error?

[davpai · Accepted solution]

I ended up using <script defer> instead of <script async>. That worked for me.