Symptoms

If there are events missing on Dashboards (lines, columns and pie charts are metrics widgets, tables are event widgets), the issue is most likely in Machine Agent or in its settings. 

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If both of these criteria are met, the connection status in /DVD/APPD_STATUS will be green.

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If despite all this no custom events are displayed under an application or a tier, it is an issue with a Unique host ID. It is caused by ABAP Agent or HTTP SDK sometimes returning a different hostname (used as a Unique host ID) than is returned by Machine Agent and they cannot be paired automatically.