Dont add the same subdomain on google custom domain

This is my experience. I have two domain: ghobro.com and riaucoding.com. It host on same hosting server. I am using add on domain feature.

First, i add this english.riaucoding.com as custom domain on my blogspot.account. Then i add english.ghobro.com. When i open it on browser, sometimes i can access it. But, mostly i get 404 error.

Now, i change the subdomain to eng.ghobro.com. Now, i dont get 404 error again. So, dont add same subdomain on your add-on domain.