We have some issues with ExternalMetricProvider:
As some scripts need more time to run for collecting data, we query them by ExternalMetricProvider instead of ExternalMetric. This works ok, but these metrics switch to "Unsupported" from time to time, if the server queries the metric immediently after a system restart and the scripts from ExternalMetricProvider have not yet finished after NetXMS agent start. If script has finished the first time after agent startup, the metrics can be pulled without error and it works fine. 

Is there a workaround to prevent this issue? I tried to switch the DCI to "Cached mode", but it looks like this does not make any difference.

There's StartupDelay parameter in agent config. Setting it to some time in seconds should prevent server connection to the agent for that time. Pls give us update if this helps. 

Thank you, I did not know about this parameter! I will report back.