Rollback Harmony firmware if your Harmony stops responding to your home automation.

Seems Harmony Hub FW 4.15.206 has a bug in it that cause the the hub to no longer respond to API requests. The simplest way to fit this it to roll back the firmware. Here are the steps that work from a  reddit post.

1. Launch MyHarmony app on PC.
2. Press Alt+F9 to open the advanced tools menu
3. Scroll the window to find your Harmony model.
4. Select "Factory Reset" for the appropriate model. This does not do anything immediately.
5. Steps 1-4 will be displayed for completing a Factory Reset. We are only doing Step 1. "Restore" here means "Rollback".
6. Connect your Harmony hub to the PC via micro-USB.
7. Within a few minutes, it will be detected by MyHarmony and display Remote Model, Firmware Version, and Hardware revision. The Restore button will be enabled.
8. Click "Restore" and wait. (Now is the first time that it actually describes that it's a rollback!)
9. When it completes, you should be on Firmware Version 4.15.193. Disconnect the hub from the PC and return it to its original location.

You might want to block WAN traffic to and from your Harmony hubs till an update it posted.

Update:12/19

Next morning my main remote was not talking to the matching hub. Tried to sync it but it seems that required unblocking the hub from the internet.

Update: 9/1/2019

They have made turning on XXMP an option the the current firmware releases. Not sure how long this is going to last but the 2 Homeseer plugins both seem to still require XXMP to work. Note when I did this the option is at
Menu > Harmony Setup > Add/Edit Devices & Activities > Hub > Enable XMPP
not
Menu > Harmony Setup > Add/Edit Devices & Activities > Remote & Hub > Enable XMPP

A quick note about POE claims and compatibility

On the camera side the specs can get a bit confused sometimes. For instance I bought some Reolinks I thought were POE from the listing but it seems the WiFi models do not support POE while the exact same models without WiFi do. You need to sort out which POE type it wants. Generally this going to be 802.3af or 802.3at but Unifi for instance has some stuff that only support 24 volt passive. And some others have they own ways of doing things so read carefully. And of course if the camera does not support POE directly but is powered by 12 volts you can always use the Huacam HCP05 Passive PoE Injector/Splitter with 5.5 x 2.1 mm Connectors. With good cables I've managed up to 200 feet with them.

You need to make sure the POE injector and the camera are the same type. The PoE Detector for IEEE 802.3 or Passive PoE - Quickly identify Power over Ethernet; Display Indicates Passive or 802.3af/at; 24v, 48v, or 56v; and Mode B Reverse Polarity is a nice cheap tester to see what is coming out of your switch. Note it sees 12 volt passive as 24 volt. Though I'm thinking something a bit more might be a good idea.

For instance I found this switch on sale. The PoE Detector for IEEE 802.3 or Passive PoE - Quickly identify Power over Ethernet; Display Indicates Passive or 802.3af/at; 24v, 48v, or 56v; and Mode B Reverse Polarity shows it is putting out 802.3at while my trusty WS-PoE-Tester - Inline Tester For Power Over Ethernet | Display 20 to 56 Volts, 0-5 Amps And Display Actively Used Power 802.3af/at and Passive PoE at 10/100/1000 Data Rates says it is outputting nothing without a matching POE camera on the other end. They have a newer version called Inline Power over Ethernet Voltage and Current Tester (PoE-Tester-Gen2) which does both. Though I'm also looking at the Triplett / Byte Brothers POE1000IL Inline POE Analyzer which seems to do a bit more.