This is expected behavior, as far as I remember, so in this case, what you can do is go to Organization > Configuration Templates.
Find the template your combined network is using.
Create a new network (e.g., a wireless-only network) and link it to the same template.
Add the new APs to this linked network.
If necessary, combine this new network with the existing combined network.
I am not a Cisco Meraki employee. My suggestions are based on documentation of Meraki best practices and day-to-day experience.
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