To tell when such a script runs, relative to Profiling log information, I inserted a timeout 600 at script top, then put it in a backup using the jobs GUI Commandline option. Instead of a delay, I got an error message:
Backup started at 1/7/2019 9:15:29 PM
Checking remote backup ...
Listing remote folder ...
Scanning local files ...
11 files need to be examined (69 bytes) (still counting)
181 files need to be examined (60.41 MB) (still counting)
402 files need to be examined (62.09 MB)
Uploading file (10.81 KB) ...
Checking remote backup ...
Listing remote folder ...
Verifying remote backup ...
Remote backup verification completed
Downloading file (1.43 KB) ...
Downloading file (11.64 KB) ...
Downloading file (15.19 MB) ...
The script "C:\<etc>\append.bat" reported error messages: ERROR: Input redirection is not supported, exiting the process immediately.
Duration of backup: 00:01:05
Remote files: 14
Remote size: 31.87 MB
Total remote quota: 231.42 GB
Available remote quota: 44.38 GB
Files added: 0
Files deleted: 0
Files changed: 0
Data uploaded: 10.81 KB
Data downloaded: 15.20 MB
Backup completed successfully!
Return code: 2
In my profiling log, the error message was between these two lines, and I guess a non-error is a silent event:
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
Maybe your script would have some similar sort of error due to the non-standard I/O environment it runs in?