For anyone that is interested, the log file got this far and then it just stopped. So I don’t think Duplicati has a way of logging when it fails. Also, I’m expecting that it could be because my backend FTP server is sometimes offline, as it is susceptible to power failures, and in the last few months have gone offline during backups or before backups started. But I’m not aware that Duplicati will crash if the backend is not up or dies during the process.
2022-03-01 01:00:18 +02 - [Profiling-Timer.Begin-Duplicati.Library.Main.Database.ExtensionMethods-ExecuteScalarInt64]: Starting - ExecuteScalarInt64: SELECT COUNT(*) FROM "FilesetEntry" WHERE "FilesetEntry"."FilesetID" = 3
2022-03-01 01:00:18 +02 - [Profiling-Timer.Finished-Duplicati.Library.Main.Database.ExtensionMethods-ExecuteScalarInt64]: ExecuteScalarInt64: SELECT COUNT(*) FROM "FilesetEntry" WHERE "FilesetEntry"."FilesetID" = 3 took 0:00:00:00.000
2022-03-01 01:00:18 +02 - [Profiling-Timer.Begin-Duplicati.Library.Main.Database.ExtensionMethods-ExecuteReader]: Starting - ExecuteReader: SELECT DISTINCT "Fileset"."ID", "Fileset"."Timestamp" FROM "Fileset", "RemoteVolume" WHERE "RemoteVolume"."ID" = "Fileset"."VolumeID" AND "Fileset"."ID" IN (SELECT "FilesetID" FROM "FilesetEntry") AND ("RemoteVolume"."State" = "Uploading" OR "RemoteVolume"."State" = "Temporary")
2022-03-01 01:00:18 +02 - [Profiling-Timer.Finished-Duplicati.Library.Main.Database.ExtensionMethods-ExecuteReader]: ExecuteReader: SELECT DISTINCT "Fileset"."ID", "Fileset"."Timestamp" FROM "Fileset", "RemoteVolume" WHERE "RemoteVolume"."ID" = "Fileset"."VolumeID" AND "Fileset"."ID" IN (SELECT "FilesetID" FROM "FilesetEntry") AND ("RemoteVolume"."State" = "Uploading" OR "RemoteVolume"."State" = "Temporary") took 0:00:00:00.000
2022-03-01 01:00:18 +02 - [Profiling-Timer.Begin-Duplicati.Library.Main.Operation.BackupHandler-PreBackupVerify]: Starting - PreBackupVerify
2022-03-01 01:00:18 +02 - [Profiling-Timer.Begin-Duplicati.Library.Main.BackendManager-RemoteOperationList]: Starting - RemoteOperationList
2022-03-01 01:00:18 +02 - [Information-Duplicati.Library.Main.BasicResults-BackendEvent]: Backend event: List - Started: ()
These are the last few lines after which Duplicati died.