Please look for context where RunScript was, as quoted earlier. Do top and bottom exist? What’s in between?
2019-01-07 21:16:34 -05 - [Profiling-Timer.Finished-Duplicati.Library.Main.Controller-RunBackup]: Running Backup took 0:00:01:05.185
2019-01-07 21:16:34 -05 - [Warning-Duplicati.Library.Modules.Builtin.RunScript-StdErrorNotEmpty]: The script "C:\<etc>\append.bat" reported error messages: ERROR: Input redirection is not supported, exiting the process immediately.
2019-01-07 21:16:34 -05 - [Information-Duplicati.Library.Main.Controller-CompletedOperation]: The operation Backup has completed
The other debug idea in the queue is the simple test. How you proceed is of course up to you, and Procmon certainly is a reasonable next step, especially with the new wrinkle of the modified script not being picked up. Keeping with the simplicity idea, you could also try modifying it to add a less complex clue, e.g. echo redirect.
I doubt it. I think this is the script start, done using Start(ProcessStartInfo). I’m not an expert in all this though.
Improvements for –run-script-before/after options which is new in beta in 2.0.4.5 seems like it may potentially affect the maybe-not-run-at-all (Procmon will say if it tried) case of --run-script-after. I don’t totally understand what it’s trying to do, but I think run might be conditional on numeric result code of the backup, which you can maybe see if you run it using the GUI Commandline option. Or try –run-script-before-required. Ignore naming.