Hello GP2, it’s a common Ethercat behavior. Devices which have a valid connection keep in OP state. But stop data exchange when at least one EC Slave is not in OP, it doesn’t matter Drive or IO. To get a more tolerant Ethercat system, each EC Slave device must be in its own SyncUnit or SyncUnit group. In a group all are affected. Details can be found here: https://docs.automation.boschrexroth.com/doc/1996056935/syncunits/latest/en/ The S20-EC-BK AD1 must be switched manual to OP again, because of its local bus. In old versions AC1 was a bug, that the S20 bus coupler must be switched to Init first and then to OP (can be seen with flashing D-LED in OP of S20 local bus). Hope this answers your observations.
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