R7800 Firmware updates 1.0.2.74, 1.0.2.76, and 1.0.2.78 disable the admin portal - broken

Please let me know if anyone has found a work around for getting the R7800 working with a firmware higher than 1.0.2.68.

I decided to updated my R7800 firmware from 1.0.2.68 to the latest firmware at the time which was 1.0.2.78.  I tried to do this via the admin portal.  Once the router restarted I kept getting ERR_CONNECTION_REFUSED when trying to get to the admin portal.  I tried this via ethernet and Wi-Fi.  I got the same behavior for 1.0.2.74 and 1.0.2.76.  Reverting back to 1.0.2.68 and all is good.

I factory reset via the pin hole and the admin portal a bunch of times before trying to upgrade in the event some of my configuration might hose up the upgrade.  No dice.

I also followed the not so helpful suggestions of clearing browser cache, disabling firewalls and anti-virus, and trying a different browser. No dice.

I found one post matching what has happened to me but it just refers to the 74 version: https://community.netgear.com/t5/Nighthawk-WiFi-Routers/R7800-update-from-nighthawk-app/m-p/1975281

Lastly, maybe this will help someone to flash their 7800 router.  Follow the instructions at https://kb.netgear.com/000059633/How-to-upload-firmware-to-a-NETGEAR-router-using-TFTP-client  but I had to do the following modifications to get it to work:

• I used the Windows TFTP client after enabling it in Windows Programs and Features
• You need to push and hold the reset pin hole button through the following stages: about 5 seconds until the power light flashes orange, disconnect power for 5 seconds, and finally reconnect power and wait until power light flashes white.  At that point you can let go of the reset pin hole button.  Now, kick off the firmware transfer from your computer to the router.  The router will do the rest.