A student used the robot and (without me knowing exactly what happened) probably smashed it on a table.
Result is that it is now in “Backdrive mode”, which to me feel a lot like some sort of back EMF (motors are can be moved manually but very sluggish).
The encoders still work and all joints are within range (+/- 2pi) but I cannot get the initialization going.
The log (at the time) read:
SafetyA One of the node is in fault mode: Base
SafetyB One of the node is in fault mode: Base
Base Logic and temporal monitoring Fault: a timing issue occurred
Base Logic and temporal monitoring Fault: a timing issue occurred
But now we don’t get these anymore.
Backdrive mode is a mode available when the robot is in its middle state of initialization (idle/standby - don’t remember).
Backdrive is made to allow people to move the robot away from tables/objects before releasing the brakes, since the robot moves a bit when releasing the brakes. The robot is in a shut down stage, but the joints will release its brakes, if they detect movement.
It will be very sluggish to move, since the motors aren’t energized and aiding you in moving the arm. 
It is enabled by holding the Freedrive button while in Idle mode.
My guess is that the Freedrive button is stuck.
If it’s not the button freedrive button that is stuck like @efn suggested. Did the student try to associate a button with the function “freedrive” in the installation tab > configuration I/O?