I spent almost an entire day of my vacation just messing around with Hue Emulation and the Alexa. Did all what you did and got those same log messages. I cleared all in /var/lib/openhab… that had hue in its name (
for i in $(find . -name "*hue*"); do rm -rf $i; done), uninstalled the binding before that, reinstalled it afterwards, …
In the end the thing that worked was - uninstall the Hue Binding (I used that to check the Hue Emulation), the Hue Emulation, delete all from /var/lib and the hueemuletion.service in /etc/openhab2, removed all [ “Lighting/Switchable” ] tags in my .items files, then upgraded to OpenHAB 2.3.0~20180329135911-1 (the latest nightly at that moment) and then installed Hue Emulation and Hue Binding and BAM - all out of a sudden after I added one lamp as [ “Lighting” ] it was discovered by Hue Emulation AND by Alexa.
Therefore I discovered that my rules are now not working since it seems in the lambdas there was a change from the “[” to “(” brackets, i.e., it now looks like this:
var lastItem = gAll.allMembers.findFirst(item|item.name.equals(itemName))
I’ve actually faced a couple of issues with that nightly versions where it seems there have been some breaking changes compared to my mid-February version I used before.
Biggest mess to me is, that though I expect a lot of people are on nightly builds, these important changes are not communicated properly or at all. That I have to use () instead of  brackets is what I only discovered by chance. I didn’t understand why the log gave me errors in my rules where these lines were in and I just by accident re-typed it with () brackets instead of  and discovered that worked. @Kai such stuff could perhaps be stated somewhere easy to see and prominent on the forum homepage?
Hope this helps you solve your issues. Keep me posted.