To clarify:
I was not referring to the use case of being on VPN and then using the Chromecast Netlfix/ youtube app, but mirroring a Chrome browser tab with "foreign" content that requires certain IP.
In that case Chromecast raises a "communication problem while on VPN" error and apparently requires some intelligent DNS modifications.

Given your location (DXB?), do you have a non-UAE IP pre-set in your router?