The Wonderware Historian with version 2017 R2 UPDATE 2 SP1 P01 was having frequent freezes of data. After around 8 hours aahEventStorage.exe seems to freeze due to an event on the A2ALMDB.
The Overall Data Rate (per sec.) in Wonderware Historian will drop almost to zero as a result and all engines on the application servers and other platforms that are reporting to the historian will go into store and forward mode.
A quick fix was applied to kill aahEventStorage.exe every 6 hours so it will be reset via a task scheduler.
When the aahEventStorage.exe freezes, the trends on all trend clients appear as a flat line until the aahEventStorage.exe is killed again.