No idea on hardware or version numbers.

EP25 from a box of 4. Other 3 work as expected. I just pulled this one out of the box and it will not add to homekit. I get "Unable to Add Accessory. An unknown error occurred." I have tried many, many times to reset the plug and add it using the instructions found at:

https://community.tp-link.com/us/smart-home/kb/detail/412486

I have not been successful. I have tried multiple iPhones and iPads. I have powered those devices off and back on to clear the Home cache. Nothing at all is making any difference in my ability to add this plug. It is brand new, just removed from the box.