Yes, think I have some other config errors with the OS X Server DNS. oh well back to IPs for now.
I’ve run into something else this morning. Got second IDF box up with MQTT client (now after forgetting client install) and relays are turning on and off via pub but not via openhab.
I changed the items and sitemap to match new switch names etc. I just added a “Underscore2” behind each switch name. So all my IDF1 Boxes are “mqttswX” while my IDF2 names are “Underscore2”. This should work I thought.
I’ve no real ideas. Could be that - is not allowed in topic names. You could use / instead. That seems to be the standard MQTT way.
I’m not sure what you are saying that you did. The names of your Items and how you put them on the sitemap is immaterial. The thing that really matters is that the connection parameters are correct in the cfg file, which they should be since you didn’t change those and the topic names must be identical in the Item binding and the sender.
Ok, I’ve finally gotten back to this part of the project. 
I took another look at my problem with the second IDF (MQTT client) not working with OpenHab. The issue was in my OH items config file. I had been using different editors I guess and a set of “quotation marks” I used OH could not read (weird). I guess I should have used OpenHab Designer from the start because as soon as I pulled it in there I saw the issue and fixed it in 2 minutes. Now all is good my second IDF is now working.
At a minimum your first thing to do when you encounter errors should be to load it into Designer. 
Glad you got it working.
Yeah, kind of one of those RTFM moments.
Here is a pic of my VERY messy MDF (cleanup after all tested and ready) :). You can see the Ubiquity switches and Gateway. The black square PC (Intel NUC) is an NVR for the security cameras. The RPi 3 hanging (fell off) is my OH and MQTT Broker. In the mounted box you can see the SainSmart 16 channel relays and the RPi 3 sitting in there is one of my RPi 3 MQTT clients running sensorReporter. The little box with RG6 is a HD HOMERUN. https://github.com/dwbro1/OG-Home-Automation/wiki