Thanks @ogiewon. Your suggestion was actually the very first steps that I tried when I first encountered this problem. Unfortunately, once I removed the switch from the device list on Alexa, I was not able to get it to rediscover even when I went through each of the steps you described. Am still not able to figure out why (this is what led me to ultimately disable then re-enable the skill in Alexa and to the whole issue with the OAuth). At any rate, I still want to thank all those that have attempted to help (I have been involved with home automation for about 30 years now but what had drawn me to Hubitat about 4 years ago as opposed to other hubs was the incredible community support available here. Again, I really appreciate everyone’s help!
PM sent, thanks!
Just a couple of thoughts...
I had a similar issue with logging back in after disabling the hubitat skill in alexa. I’m not entirely sure how I solved it because It was quite late at night and I don't recall the exact sequence In my sleepy haze I didn't think to document what I was doing.
For what it's worth, while I was having this trouble with Alexa and Hubitat, there was also an oauth issue with some node-red users (me included) that broke alexa related flows. I was able to fix that with a creative workaround involving getting a new cookie from amazon to put on my Rpi that I use to run node-red.
I suppose these problems could be happening because of "updates" to the Alexa API, but I'm not aware of any specific changes. There are many people here who would know much better that could speak to that. Given the issues I experienced, it seems alexa was the common denominator though.
I had to do this once, many years ago, in order to get Hubitat Contact and Motion sensors to properly work as Triggers in Alexa Routines. I have recommended this procedure as a last resort to a few other users over the years and it does seem to solve issues for many users.
WARNING - THIS IS A LAST RESORT! use at your own risk!
- Open the Alexa App on your mobile phone. Disable the Hubitat Skill and then manually delete ALL Alexa Smart Home devices that are from Hubitat.
- Remove the Hubitat Hub's "Amazon Echo Skill" app.
- Open the Alexa App on your mobile phone. Enable the Hubitat Skill, sign into the Hubitat cloud, and select your hub. This will AUTOMAGICALLY install the "Amazon Echo Skill" app on your Hubitat hub and will allow you to select Hubitat devices. Be sure to click save/done.
- The Alexa App on your mobile phone should 'see' the devices and allow proper control of them.
Again, this is the 'Nuclear Option' and so it is not recommended as an early troubleshooting step. It is a last resort. Use with extreme caution and don't blame me if things end up worse than how they started! 
lol, I actually just edited that out of my previous post because I didn’t want to cause someone to nuke their setup based on my comments. Thanks for posting the sequence; that makes me feel better about mentioning it.
I just recently started having this problem on my C-8 running firmware 2.3.9.166. I've upgraded to 2.3.9.177 (most current) but of course it looks like it will be a week to find out if it worked. I this "last resort" process the only way you know of to resolve the problem?
I also saw a post about setting up an automation to reboot the hub once a week, but when I try entering any variety of the command "http://[ipaddress]:8080/hub/reboot" I get a response of "Not found".
If just updating (and thus rebooting) your hub fixed it then it is likely that your hub just got disconnected with the HE cloud system, which was an issue that has been happening recently. They think it is is fixed in the 177 build. You may not need to take any other action.
I had rebooted it this morning just to get it working, then a short time later did the software update. So it sounds like a week from now I'll know if the update worked.
