The mycroft sd card image is created with Debian Jessie Lite. Apparently the Jessie release of debian does not support some of the hardware changes in the B+ and there has been limited success getting mycroft to run on Debian Stretch, something to do with a Python OpenSSL error I think.
More information here Raspberry Pi 3 Model B+ Compatibility?
and here Picroft Survey 2018 – Results and Roadmap implications