This is copied from the OpenWRT Page concerning your router:

Wired stations cannot ping each other

This is a known bug: "switch eth0(Atheros AR8316) no traffic between ports possible" Based on the comments from the bug you can try these commands:

swconfig dev eth0 vlan 1 set ports "0 1 2 3 4 5"
swconfig dev eth0 set apply

If these work you can add the following lines to your /etc/config/network:

config switch
  option name 'eth0'
  option reset    '1'


config switch_vlan
  option vlan '1'
  option device   'eth0'
  option ports    '0 1 2 3 4 5'

What you can do on the Android devices:

Network Tools can do a traceroute.

ipconfig will show you more network settings (like the gateway and lease duration) than the standard menus.

See what those settings are to determine whether DHCP is handing out the correct info or not.

If it looks like the device does have all the correct info (same as when you manually apply it and it works) then do the traceroute and see if that reveals anything about what the device is doing.

What you can do on the DHCP server:

In the DHCP manager, right click on IPv4, choose Properties, then go to the Advanced tab. You should see an Audit log file path which defaults to %WinDir%\system32\dhcp.

In that folder you should have detailed logs, one for each day of the week. That should help you determine what's going in a particular request.

In Event Viewer, browse to Applications and Services Logs > Microsoft > Windows > DHCP-Server. The logs in here show errors related to specific MAC addresses and requests, could be helpful.

In DHCP manager, under IPv4, check Filters and Policies to see if you have anything set in there that might be excluding Android devices (or any other settings that look interesting). For example, all android devices have a hostname that begins with Android- so you could create a policy that gives any client with an FQDN beginning with Android a different router.

Have you posted all of the DHCP options in effect (global and scope)?