This issue has been detected in UIM 8.4 SP2.
In some cases, the Alarm Enrichment probe stops processing alarms and messages start being queued.
The AE logs show the following repetitive message:
Jan 25 02:59:00:962 [attach_clientsession, alarm_enrichment] AlarmQueueReader alarm count waiting for alarms to be flushed
Jan 25 02:59:20:963 [attach_clientsession, alarm_enrichment] AlarmQueueReader alarm count done waiting for alarms to be flushed time: 20000
A workaround to get the AE probe back to normal operation is to restart the probe.
The solution is to upgrade nas to 8.42 or later, robot to 7.80 HF21 and hub probe to 7.80 HF22
And add the following keys in the nas and hub probes.
lower_memory_usage_threshold_percentage = 0.90
upper_memory_usage_threshold_percentage = 0.90
memory_usage_exceeded_threshold = 3
post_max_age = 60