Adding multiple subdomains causes issues. The subdomain.domain.com page takes time

I am trying out a feature in my website where each user has his own page like - user.domain.com.
My site is configured on AWS cloudfront and the DNS management is via Cloudflare.
So for a new user, say user1, I will add a CNAME record user1 (via Cloudflare API) and point it to my cloudfront site. The page - user1.domain.com works instantly Everything work perfectly fine until my CNAME records reach around 120 and after that every subdomain added, the page doesn’t work instantly and takes time. So, say I add user2 the user2.domain.com shows 404 and starts working after 10-15 mins.
Can someone please tell me why is this happening? I am trying this on QA site with a free Cloudflare account. Is that the problem?
Thank you for reading this.

What DNS servers are you using on your devices?

10-15 minutes for DNS propagation isn’t unheard of depending on whose servers you’re using - the default ones provided by ISP’s are notoriously slow in a lot of cases.

Or an alternative method, is there any reason you couldn’t just use a wildcard record & configure a ‘not found’ page on your origin if you haven’t configured the user.domain.com site for that address?

Thank you for the reply.

What DNS servers are you using on your devices?

Google DNS

10-15 minutes for DNS propagation isn’t unheard of depending on whose servers you’re using - the default ones provided by ISP’s are notoriously slow in a lot of cases.

I agree. But, I think there is something with too many subdomain issue going on here. I say this because it works perfectly fine with around 120 subdomains and then starts creating issues. Say, if I delete a couple of subdomains and add a new one, it works perfectly fine again. A lot of sites like zendesk, etc instantly create a page for their user. Do they do something different ?

A 404 is an HTTP response from your origin server. Seems unlikely to be Cloudflare related.

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