Cloud data sync failing

All games fail to sync cloud data on all profiles on all consoles on my home network. I've tried quite a few solutions, and none have worked. Two of the three games I play (BO3 and Smite) I can select the option to use offline data, wait at the menu a second,
and then continue playing online as usual. However, using offline data for ESO gets me stuck at the main menu with a "Loading Profile Failed" error. Everything else works fine, store, apps, playing online after bypassing the sync fail. I've contacted my ISP
(Time Warner Cable) multiple times and they've assured me that my modem's signal is good, no ports are blocked, and there's nothing they can do to help.

Here are the things I've tried (with plenty of hard-reboots mixed in):

1. Opened ports on the router
2. Deleted local save data
3. Deleted cloud save data
4. Going offline in network settings, restarting console via snap menu, going online and letting the game sign me in.
   
5. Using my phone's hotspot to sync data (it works fine this way) then plugging in ethernet cable after being connected. On ESO this kicks me back to the menu and square one.
   
6. Deleted profile
7. Tried another profile
8. Cleared alternate mac address
9. Cleared persistent storage
10. Setting network settings to automatic and hard resetting router
11. Bypassing router entirely, only using the modem (and the modem doesn't have any configuration to set or change)
    
12. Reinstalling the games
13. Restoring factory default settings
14. Using Google's public DNS
15. Buying a new xbox

I'm positive I'm forgetting a few things I've tried, but that's most. Currently the only way I can play ESO is to use my phone's hotspot and connect through Verizon. My modem is a Motorola SB6121 and my router is a TP-Link WR841N. The network tests on the
xbox report that nothing's wrong. I have open NAT on my home network and strict NAT on my hotspot.

Any help is greatly appreciated. I'm running out of data on my phone plan T_T

:)

 

Cloud data sync failing.

Nothing in that thread applies to me. It seems to be a thread about a bad router configuration, and problems with his NAT.

 

Cloud data sync failing.

I am having this exact problem. The only way I can get cloud saves to sync is via my phone's hotspot. All other network functionality, both on XboxOne and other devices, works great via my normal Centurylink DSL connection. It's just Synced data that's horribly
slow and then fails. What does data syncing do differently than other network activity that clearly does not work with some ISPs?