I have identified the problem and found a solution. The problem is my router, the Netgear C6300 (combo router and modem). My phone is a Verizon Samsung Note 5. My wife has a Samsung Galaxy S6. Both worked fine on our home network until the new Marshmallow 6.0.1 was downloaded. Once the new software was installed in both phones, neither would connect to Netflix or You Tube and neither would download apps from Play Store from our home network. 4G worked fine. The solution is to set up a secure guest network in the router for the phones to access. For some reason they won't work on the regular 2.4GHz b/g/n or 5GHz a/n wifi networks. Here's what I did (from the User Manual):
Set Up a WiFi Guest Network
A guest network allows visitors at your home to use the Internet without using your wireless
security key. You can add a guest network to each wireless network: 2.4 GHz b/g/n and
5.0 GHz a/n.
To set up a guest network:
1. Launch a web browser from a computer or wireless device that is connected to the
network.
2. Type
http://routerlogin.net.
A login window opens.
3. Enter the modem router user name and password.
The user name is admin. The default password is password. The user name and
password are case-sensitive.
The BASIC Home page displays
4. Select Guest Network.
5. Select any of the following wireless settings:
• Enable Guest Network. When this check box is selected, the guest network is
enabled, and guests can connect to your network using the SSID of this profile.
• Enable SSID Broadcast. If this check box is selected, the wireless access point
broadcasts its name (SSID) to all wireless stations. Stations with no SSID can adopt
the correct SSID for connections to this access point.
• Allow guest to see each other and access my local network. If this check box is
selected, anyone who connects to this SSID can access your local network, not just
the Internet.
6. Give the guest network a name.
The guest network name is case-sensitive and can be up to 32 characters. You then
manually configure the wireless devices in your network to use the guest network name
in addition to the main SSID.
7. Select a security option.
The WPA2 options use the newest standard for the strongest security, but some older
computers and wireless devices cannot use it. NETGEAR recommends that you select
the WPA-PSK [TKIP] + WPA2-PSK [AES] radio button. This setting protects your WiFi
network and lets computers and wireless devices connect to the WiFi network by using
either WPA2 or WPA security.
8. Click the Apply button.
Your settings are saved.
I enabled the SSID broadcast and set my security to WPA-PSK [TKIP] + WPA2-PSK [AES]. Both of our phones are working perfectly now on our home wifi network and we're still secure. The big question of the day for me is for Samsung: What did you add to the Marshmallow update that caused our phones to stop working on our home network? The only thing that changed was the phone software. Nothing in our wifi network changed.