Events from group may have been lost due to a collection failover
Unlike events, alarms are never stored on disk by System 800xA. Alarms are considered "fresh info" and is never cached on disk between startups, etc.
The alarm manager uses a refresh function towards its event collectors, which in turn uses OPC AE Refresh() call towards the OPC AE servers that have been configured. Not all OPC AE server support refresh. So for some connect families, e.g. AC400 Connect, the alarm list will be empty after a complete restart of all CS and AS nodes.
I believe the "Events from *someeventcollectorgroup* may have been lost due to a collection failover." diagnostic event becomes triggered if the alarm manager refresh towards the event collector return zero (0) alarms.
I have seen this occur even if no alarms have been generated during the downtime (and no alarm loss should be possible), i.e. the warning is false.
If you have trouble with this indication and seek a correction, please ask your regional ABB support center to submit a support case.