At about 5:40pm yesterday, the EtherCAT system stopped communicating with BIO chassis 1&2. Inspecting the chassis in the CER, chassis 1 has an LED in the back indicating that +24V is off, whereas the LED in the front indicates that +24V is on. Things to try:
Fil and I went with a laptop to check, if we can make a connection to the individual chassis. This worked and it turned out that the Ethernet cable between the EtherCAT chassis and the first chassis was broken. A strange failure mode, but it seems to work again.