Issue Detail

Lot of logs in Event Viewer related with "Scheduler Exception -Sequence contains more than one matching element". This occurs when there is a duplicate entry in the WebServers table.

Solution

To verify if this is the issue, go to Host > SQL and run the following SQL query: 

SELECT ServerName FROM {databaseOwner}[{objectQualifier}WebServers]

If you see the same entry more than once, you need to run the following SQL query: 

DELETE FROM {databaseOwner}[{objectQualifier}WebServers]

Once that has been completed, hover over Tools->Recycle Application Domain to make it work with re-indexing.

Referrence

Scheduler Issues in DNN 7.3.x

Scheduler exception after Upgrade to 7.3.0

DNN 7.3.1 SCHEDULER EXCEPTION