No exceptions are thrown in case of inconsistency in the update flow issued by the Data Adapter.
This holds for all kinds of possible inconsistencies:
  • about the values of the special "key" and "command" fields in COMMAND mode;
  • about the sequence of ADD, UPDATE and DELETE commands in COMMAND mode (which is your case);
  • about the sequence of snapshot and real time updates.

In those cases, either the event is discarded or it is interpreted in the most likely way and forwarded. Only a log message at WARN or ERROR level on LightstreamerLogger.preprocessor is issued as a notification.

Note that the recovery policy has slightly changed in the transition from 3.5 and 3.6 version of the Server, towards a more tolerant policy.
However, it is still possible that unexpected events are eventually lost in the subsequent stages.
Hence, inconsistent sequences of events are still discouraged and not officially supported.

I confirm that there is no facility for checking the current set of keys for an item in COMMAND mode from the Data Adapter,
therefore, the consistency check are entirely charged on the Data Adapter.