When syncing Salesforce activity to Timeline, records that do not have a value in Description/Comments will fail because It is mapping to Notes in the Timeline Activity which is a required field. It fails because Notes has to have a value in order to save.
If there was a way to provide a default value for Notes when the incoming record from SFDC has a null value for Description, that would make it easier to sync data without having to find records in the logs that failed and update. Having the option to set default in the job setup would allow for a default Notes value specific to the type of Salesforce activity being synced.