Seems like routing might be getting in the way. Can you set it to bridge mode? Make sure the gateway in the dhcp range and in the server isn't getting in the way. Seems like you might want the server to be in the same subnet.
For a quick and easy setup, set it in bridge mode and put everything on the same subnet.
If I were doing it for like a portable game server (not sure what your use case is), I would set my static ip address on the server to something like 192.168.0.2/24 with a gateway of 192.168.0.1. Then set the "external interface" on the router (interface for the web server) to 192.168.0.1/24.
Then set the dhcp range to 192.168.1.10-20/24 with a gateway of 192.168.1.1. Set the "internal interface" (wifi) on the router to 192.168.1.1/24.
Normally, something like this setup would not allow anything from the web server to initiate traffic to the clients. Only the clients could initiate. If you want the server to be able to initiate traffic, there should be a firewall setting in the router to open it up.
Just thought of another possible cause..... check your internal firewalls. Make sure you're allowing inbound communication.
