Update: Left for 5 hours, nothing happened. Reset the device (as it was still downloading, not installing), started downloading again and got stuck at the same place overnight.
Is there any sort of network issue preventing the complete update?
I feel your frustration. I had similar issue with my new Gen 4 device. In my case, I went through the entire setup with little/no problem. Came back next morning to verify how many channels were found and the app on my phone could not find the Tablo Gen4. Had solid blue LED. I tried unplugging (power reset), reset button underneath, Factory reset; every attempt resulted only in Solid BLUE LED and no response from the Gen4. Ultimately, I called @TabloSupport , they went through some trouble shooting steps, had me send a short video of trying to reset and only solid blue LED, tehn shipped me a replacement device overnight express.
Hopefully, doing some troubleshooting and resets will get you back on track and you won’t have to do a replacement, but don’t give up. Good luck and let us know how you got this issue resolved.