S6 won't find and/or connect to WiFi that is has been connected to in the past

[jersno]

I have a TP-Link router with a 5GHz Wi-Fi setup without broadcasting the SSID (Not using Dual Band mode). My S6 was connected to this network from June 2015-November 2015 with NO issues at all. I went on vacation for a few months and when I came back, my S6 will no longer connect to this network. My iPhone 6 in the same scenario, picked the network back up and it is working fine on it, so I don't think it is the network or Wi-Fi settings.

I have tried:
-Changing non-broadcasted SSID network password and SSID to something new. No Love.
-Broadcasting the old and new SSID (the S6 will not see broadcasted SSIDs, but other devices do and connect normally). The S6 sees many other WiFi networks, but not either of mine when broadcasted
-Broadcasting the 2.4GHz network. Same issues as above.
-Connecting to the 2.4GHz network while not broadcasting SSID. No Love.
-Restarting phone and router multiple times
-I have used a third party Wi-Fi app (WiFi Manager) to forget the network (and all old networks) from my phone. I then re-added the hidden SSID network . No love.

Fully updated T-Mobile S6 with Android Version 5.1.1 and non-rooted.

I posted this as a guest in the question/answer section, but figured I'd get better answers from a thread. I apologize in advance if this is double posted because of that.

 

[sydneycooper1979]

Have you reset the router?

 

[jersno]

Reset it to factory defaults? Nah, not yet. I was hoping to avoid that since every other device I have works fine with it, but will probably give that a go today.

 

[jersno]

No love after resetting my router either.

When I add the network manully on my S6, I can go into the third party app, WiFi Manager, and see it under known networks.
When I click on it, It is listed with:

• Level: 0%
• Channel: ?
• BSS: ?
• Security: WPA/WPA2

When I try another known network, It displays a message that says it is out of range, so I assume that means I can see my current network.

Also tried to broadcast the SSID once the router was reset. S6 never sees the network, but other devices do and connect.

IPhone connected just fine once the router was reset and the WiFi was recreated.

 

[jersno]

FYI if someone else runs into something like this... I set up a 2.4GHz hidden network and set my router in Dual Band mode. This allowed me to connect to the 2.4GHz hidden network with my S6.

I still have no idea why it can't connect to the hidden 5GHz network it was connected to for 5 months prior or can't see the 5GHz if I broadcast the SSID now.