Google Cloud DNS giving 404 on top level domain

I’m using Google Cloud DNS and Google App Engine Standard to configure an application.

Currently, I configured the DNS like this

mydomain.com.   A   300  216.239.32.21 216.239.34.21 216.239.36.21 216.239.38.21  mydomain.com.   AAAA    300  2001:4860:4802:32::15 2001:4860:4802:34::15 2001:4860:4802:36::15 2001:4860:4802:38::15  mydomain.com.   MX  216000   1 aspmx.l.google.com. 5 alt1.aspmx.l.google.com. 5 alt2.aspmx.l.google.com. 10 alt3.aspmx.l.google.com. 10 alt4.aspmx.l.google.com.  mydomain.com.   NS  21600    ns-cloud-c1.googledomains.com. ns-cloud-c2.googledomains.com. ns-cloud-c3.googledomains.com. ns-cloud-c4.googledomains.com.  mydomain.com.   SOA 21600    ns-cloud-c1.googledomains.com. cloud-dns-hostmaster.google.com. 1 21600 3600 259200 300  @.mydomain.com. A   300  216.239.32.21 216.239.34.21 216.239.36.21 216.239.38.21  api.mydomain.com.   CNAME   300  ghs.googlehosted.com.  stage.mydomain.com. CNAME   300  ghs.googlehosted.com.  api.stage.mydomain.com. CNAME   300  ghs.googlehosted.com.  www.stage.mydomain.com. CNAME   300  ghs.googlehosted.com.  www.mydomain.com.   CNAME   300  ghs.googlehosted.com. 

So that I configured an stage environment using these domains and it is working so far.

  • api.stage.mydomain.com
  • stage.mydomain.com / www.stage.mydomain.com

I recently added the configuration for production with these domains

  • api.mydomain.com
  • mydomain.com / www.mydomain.com

And it is working so far except that mydomain.com is returning 404 http status from Google:

404. That’s an error.  The requested URL was not found on this server. That’s all we know. 

Does anyone has encountered this problem before? How can it be solved so that mydomain.com starts working?