SharePoint monitoring is very necessary and should be done on a regular basis as it will give complete idea about any exceptions/errors/if any services are not running/if any servers are not responding etc. While monitoring the servers the following errors appeared in the event viewer:
  • Event 5239 (Excel Services Application) of severity 'Error' occurred 10 more time(s) and was suppressed in the event log
  • Event 5231 (Excel Services Application) of severity 'Error' occurred 10 more time(s) and was suppressed in the event log

To verify, try opening Excel dashboards on each server (WFE’s) to find out which server is the culprit. Before doing this, make sure that the Excel service application is in start mode as well as the app pool is running.

Coming back to dashboard point, you will find the culprit server. Just restart that specific server and check the results. In this case it fixed the issue and is referenced below:

The above article will be indeed be helpful in many scenarios:

  1. Delayed load times for workbooks.
  2. Workbooks fail to load.
  3. This event appears in the event log: Event ID: 5231 Description: Unable to reach Excel Calculation Server [Session: User: ]

Possible resolutions:

  1. Restart Excel calculations services
  2. Recycle app pool
  3. Make sure that the account you are using for Excel calculation service is working properly (i.e. not locked)
  4. Reboot the server