Mapped Domains is not resolving properly

Hello Support,

I hope you're having a great day.

On the domain I'm reporting on I have two subdomains setup. One is working (re-directing to the mapped URL from the subsite) and the other is not. (This is happening across all of my networks, I'm not sure when it started as I don't visit all of my sites all of the time).

They resolve at the specified mapped domain but they don't redirect when entering the subdomain url even when selecting 'Mapped Domain'.

Thank you for your assistance.