There could be a number of reasons why you’re not seeing the expected data. Here are some possible situations you might need to check.
The first thing to verify is whether the GA4 tracking code is properly installed on both of your subdomains. This is the most common reason for not seeing any data. You can check the source code of your pages or use tools like Google Tag Assistant to verify this.
Secondly, it’s also possible that you’ve set up some filters that are excluding the data from these subdomains. Be sure to check any filters you’ve set up in your GA4 property to ensure that they’re not inadvertently blocking data.
Lastly, keep in mind that there is usually a delay of up to 24 hours before data start showing up in your reports. This is particularly true when you first set up a new property or view. So if you’ve recently made these changes, it might just be a matter of waiting a little bit longer.
Remember too that GA4 uses different data models than Universal Analytics, so your subdomain traffic might be located in different report sections. If there are specific user interactions on your sub-domains that you’d like to track, you may need to set up custom events for these.