Several users reported that mhuxd can’t connect the microHAM keyer and marks the keyer as OFFLINE under some circumstances. It has been turned out that the package “modemmanager” is the cause of the problem. It connects to each newly connected USB-serial device, changes baud to various values and sends modem AT commands.
If you don’t need “modemmanager” then remove it. On Debian & Ubuntu by:
sudo apt-get remove modemmanager
If you need “modemmanager” you can wait for the next mhuxd update. Or you can replace /lib/udev/rules.d/59-mhuxd.rules by this file: