(OK) Android devices don't know route to a host located in the same network
Not sure that this is your problem, but some wifi routers and access points have a feature called "Station Separation" or "Wireless Isolation", that restricts connected devices from talking to each other. When this feature is enabled, the access point will not route packets between different connected devices: only between devices and the uplink port.
The feature is intended for business networks offering guest access, where services like printers, servers, and network shares are all connected via the wired lan, so you don't really need wireless-wireless communication, and it helps keeps guests separated from the sensitive business network.
