Observation suddenly stopped with the message "EMERGENCY STOP (Forced to stop) / Lost control priority." on the Manager GUI
COSMOS3 communication between the ASTE and remote sites was cut due to some (unknown) reasons. Just take the priority again by pushing the "THIS NODE" button on the Manager GUI, and you will be able to restart your observations.
All local controllers (LOC) are "NO RESPONSE" on the Local Controller Activity GUI and there is no response from the GUI even if you click one of the LOCs.
The LOC GUI sometimes freezes. Kill it using xkill (type 'xkill' on a terminal) and then, restart it.