Site sometimes renders as code

I have a site that I put made for someone using Grav, She has contacted me to tell me some of her customers are reporting that the site sometimes renders as just code instead of the website. I have no idea how to go able tracking down the issue and was hoping that I can reach out and find some help here. I’ve asked her to grab a screenshot if she can recreate the issue or if it happens again. I don’t know if the problem could be related to Grav or related to the hosting account. The website is hosted with GoDaddy. Any help would be greatly appreciated.

I see nothing in the site’s code that would cause CSS not to render, only console error is a 404 for the favicon. You might want to test it in a broader variety of browsers to see if anything is amiss.

Maybe the missing doctype

Thanks for the responses. Also, thanks for the link to the w3c validator; I didn’t know that was there.