This may be dumb, but can you set your phone's DNS manually to 8.8.8.8 and 1.1.1.1 for giggles? Just to ensure DNS is properly seeing things?
LOL, you really put me to work because I wasn't sure what that was and how to do it. A quick search gave me the explanation and how to proceed. Unfortunately, after switching to static IPs on both the phone and hub (and rebooting the hub) I once again I got the 404 error on Google Home. Thanks for the suggestion because I want to try everything.
I'll also use this opportunity to give an update on my status with Google tier-2 support. I received an initial email that said they would need 24-48 hours to investigate. Then (last week) I got a follow-up email asking for much more detailed information including a video of an attempt to connect to 'Works with Google' on my phone. I provided all of the info and the video. Today I got another email saying they would follow up with me when they have more information. It was nice to get confirmation that it was still in the works.
What's the use of life if we aren't learning... 
Do you have another Google/GMail account that you could possibly use for testing purposes? If you could use a completely different smart phone, with a completely different Google account, and then try connecting the Google Home App on that phone to your Hubitat hub, that would be a good test. Please be sure to remove the "Google Home" app from the list of Installed Apps on your Hubitat Hub before attempting this test. The "Google Home Installation Helper" app is just a set of instructions. You do not need to install the "Google Home Installation Helper" app on your hub in order to link Google Home to your Hubitat Hub.
Simply adding the Hubitat integration within the Google Home app on your phone, and then logging into your Hubitat account, will automagically install the "Google Home" app on your Hubitat Hub.
Sounds like a great idea but unfortunately I only have one Google account. I do have another device (a tablet) that operates on wi-fi only. I don't think I'll get another account while I wait for Google to offer their response. I'll keep your idea in mind and may proceed if all else fails. Thanks
You can create another Google account in 30s and then give @ogiewon's suggestion a try in just a few minutes. Up to you, of course, but I don't see Ogie's suggestion as an "If all else fails" activity.
Did you add the DNS entries?
Yep, I set the DNS to 8.8.8.8 and 8.8.4.4 (and re-entered the original IP and gateway so Save would actually work). Still got the exact same 404.
So at least we can cross DNS caching off the list of suspects. One less rabbit hole! Thanks for the idea though, it was definitely worth trying.
You've tried doing this from a PC as well right? Not just your phone? Or tried using another phone?
Thanks for sticking with me on this challenging situation. As far as I know the primary way to add a "Works with Google" device is on a mobile device (Android or iOS), but not natively on a PC. I suppose I could add an emulator on my PC but that seems to be a bridge too far because the optimist in me says there will be a simpler solution/fix from Google.
Keep em coming and keep me thinking.
Have you done both android and ios?
Nope, I only have Android.
See if you can get an iphone or ipad to try
I may do that but help me think this through.
- Would that require logging into my account on someone else's phone?
- If it succeeded would it prove that IOS is better than Android for this?
- Would it mean that person needs to give me their device because I need it
.
On a serious note I'll try most anything if it will get my current phone, Google account, and HE operational with Hey Google. I'd rather not do things that just prove a point, but don't get me that result.
Yes but you can log out and it doesn't save the credentials
No but if it works you could do the initial setup and figure out the android issue later
Only for the initial setup
I was having a little fun on the last post but this is a serious question (perhaps a dumb one).
If I get the authorization (pairing) done on an iPhone, and then delete the credentials, would that leave my hub and Google connected.
Yes
Wow, this could be huge, thanks. I'll try that ASAP (but it might be a few days).
I guess I'm in the minority. Clicking on "Authorize" in oauth.cloud.hubitat sends me to a 404 error for oauth-redirect.googleusercontent.com
Lots of folks have offered some great suggestions in this thread. Perhaps one of those will work for you.