Website not rendering reliably

I’ve been using Cloudflare since 2018 for serving a website of mine that is running on heroku at This has been running without a hitch since I set it up, but suddenly I now notice that the site is not rendering properly on the domain that Cloudflare is managing.

For instance this page consistently renders perfectly on

But is very intermittent on

see image below that is missing the logo and navbar:

I’m completely at a loss to understand why this is and don’t know how to start diagnosing it. There are no network or console errors when I view the page in Chrome Developer tools. Any advice appreciated please

Thanks in advance
Nick Barrett