I have Samsung T900 Tablet but I have just done a hard reset and it is still not connecting to the internet. It has full Wifi access but refuses to see the internet of even the router via a browser. Even the initial start-up EULA does not see the internet when it is connected to the wifi.
All my other devices can access the internet and there is no blocking of this device on the router.
And without internet access, I cannot update any software etc.
I have tried using a wifi hotspot on my phone and it connects. But anything using the wifi direct does not connect to the internet or the router webpage.
So it works connecting to your phone but not to your modem. Then it still has to be something involving the mode.
Have you checked if the tablet is using 2.4 or 5.0 MHz? And what the browser is broadcasting as well. Which one? That would make a huge difference as a device that can only access one of them (some can access both) will only be able to access a connection that is also using that.
So if say your modem is broadcasting at the newer 5.0 MHz but the tablet is older and only can access 2.4 MHz, then they can't see the signal. The same goes for the reverse.
You will need to check both of these on both devices.
Additionally, while your modem/router may not be blocking that specific tablet, it could be limiting the number of devices you can connect. So I would check that as well.