Evidently a problem with the Harmony, it has been happening to me for most of a full day now. Started having problems last night and it carried over this morning. I went in and "sync'd) the Harmony bandit had no affect at first, but after about 5 minutes everything started working correctly again. I think it updated over the last couple of days. Also, if you use YONOMI most of what it used to aid in really doesn't add any greatness to the Alexa/harmony experience any longer. When I first started using it, YONOMI was almost required for some commands. Now, not so much.
Currently, I can get all of my standard use Harmony commands to work. I also found a bunch of new commands out there for Harmony and for Alexa and Fire Stick... can't find them for this post, but I looked at the stuff on Amazon and it doesn't show all the commands I was seeing earlier... I'll have to dig some to remember where I saw the commands listed... some were how to navigate such as navigating upend down on the screen and left and right and such... but I didn't save the page... Should have printed it when I found it. It was full of gems.
The last thing I did while typing this line was to ask "Alexa... Turn on Fire TV" and she did it with no hesitation or lag. Just like normal. This is the most common command form all of us in the house. That and "Alexa...Turn everything off" which was having a hard time as well...
Try the Sync and let us know how it works for you.