RBR750/RBS750 - satellites won't connect to mesh network

Download latest firmware for your devices from netgear.com/support If you have the RBS750 and RBR750, those are the links. Unzip both files:
https://www.netgear.com/support/product/rbr750.aspx#download

https://www.netgear.com/support/product/rbs750.aspx#download

Important Notes:

• To do the process below, you need to be connected via ethernet between your computer and the router, do not do this over Wi-Fi,
• Update satellites firmware first, and then your router last.

Here is what I did to resolve it:

1. Unplug everything (power and ethernet), plug ethernet between your computer and the router, then power back to the router only. Let the router start entirely,
2. Reset the router by pushing the 'reset' button with a pin at the back of the router for 15 seconds; wait for the router to start completely (solid white or not light at all),
3. Once the router has started, set up the router so that you can access it via the admin interface (this is normal configuration via web admin or mobile app),
4. Update the satellites firmware:
   1. Plug ethernet cable from one satellite to the router, and plug power to the satellite; wait for the satellite to start completely (solid blue),
   2. Push 'reset' on the satellite to reset the device and wait for solid blue light,

   3. Once solid blue is visible, go on router admin via web interface and go to 'Attached Devices'. You should see a "netgear" device via 'wired' in the list under "Connected Devices". Note the IP address and open it in a new tab,

   4. Login using your the credentials you used in step 3. If those don't work, try the default admin/password ("password" is the actual password) which worked for me; from there you should see the firmware version,
   5. If the version is not the same as the one downloaded earlier, go to 'Firmware Upgrade', then 'Browse' and select the .cfk file from the RBS-750 (pick RBS, not RBR), and let it do its jobs; the satellite will eventually reboot, it takes a little while,
5. Unplug ethernet and power from your satellite and repeat step 4.1 to 4.5 with every other satellites you have.
6. Once done, it is time to upgrade the router firmware:
   1. Disconnect all satellites from the router, unplug power from satellites; your computer is still connected to router via ethernet,
   2. In the router admin interface, go to "Advanced" tab > Administration > Firmware Update > "Manual Update" tab,
   3. Click "Browse" and select the .chk from the RBR-750 folder (not RBS), click "Upload" and let it do its job, until the router restart and shows no light (or solid white).
7. Plug power back to satellites (no ethernet); they should automatically sync with the router (show solid blue light). It take a little while.
8. Once both satellites show a solid blue, go to the router admin interface > "Attached Devices"; you should now see both routers in the "Connected Satellites" section (not in the "Connected Devices" section anymore).

And that, should resolve the issue of satellites not connecting to your router. The whole process takes a little while, especially when you reset/reboot devices as they take a few minutes to be ready. Any questions, please feel free to ask in this thread. I will try my best to help.

A bit of background: this issue has been caused by Netgear themselves. They pushed an update to either satellites or router without pushing the update to the other device, as such devices were using different firmware versions and were not able to properly sync. To me the issue started around May 25th.