Prerender.io's cached html header getting replaced by static header

Start by comparing the Express Prerender.io middleware behavior for the Heroku URL and the Namecheap domain. Reproduce the differing meta tags with Facebook Debugger, metatags.io, and curl using the Googlebot user agent, then inspect the middleware and domain configuration to identify where the static index.html header is returned. Done means explaining the domain-specific difference and documenting a verified fix.

I have a Heroku app that I added a namecheap domain (https://www.platonic.chat/) to. I recently added SEO to the app using Prerender.io, so particular pages on the app have dynamic link preview. However, the namecheap domain does not display the desired dynamic link preview. I can see on my Prerender.io dashboard that it cached the pages correctly, but somehow the <meta> tags of the cached htmls got replaced by the <meta> tags of the static index.html when the cached htmls get fetched.

Another observation is that the Heroku domain that doesn't use namecheap (https://platonic-prod.herokuapp.com/) doesn’t have this problem. In the Heroku domain (https://platonic-prod.herokuapp.com/c/welcome-to-platonic), the desired title meta tag is:

<meta property=“og:title” content=“Welcome to Platonic”>
.
.
.

But in the namecheap domain (https://www.platonic.chat/c/welcome-to-platonic), the title meta tag is:

<meta property=“og:title” content=“Platonic”>
.
.
.

The body of the Prerender.io fetched html in both cases are the same, so it seems to me that something is replacing the header of cached html. The link preview gives the incorrect result when I use Facebook Debugger and metatags.io, but it gives the correct result when I use Googlebot through command line curl -A Googlebot https://www.example.com/ and displays properly on Discord. So why does adding a namecheap domain to a Heroku app modifies the cached html when it gets fetched?

I am using ExpressJS middleware for Prerender.io, caching Angular pages.