I just spent at least two hours trying to figure out how to get the Arduino Pro Micro running again. I will spare you the details of how I figured out what to do, so here is the solution:

sudo mv /usr/share/dbus-1/system-services/org.freedesktop.ModemManager.service /usr/share/dbus-1/system-services/org.freedesktop.ModemManager.service.disabled

Lets hope it keeps on working :-)