Hi there,
I already searched the forum and the documentation, but I wasn’t able to find any information about how Duplicacy exactly behaves if changes to a repository occur while backup is in progress. Is there any documentation available? If so, a link would be greatly appreciated. 
Thank you very much for your help!
There is no documentation about this particular subject.
The way 
works is just like windows copy: it enumerates all the files and folders at the start of the process, then does the work. If at any point a file/folder is missing will log that the file is missing and carry on (windows copy stops and asks you if you wanna continue/resume).
If you want to take a real snapshot of the filesystem, you should use the -vss option when running backup. (though not all programs follow this mode correctly - ymmv)
Thank you very much for the quick response and the clarification. Question solved 
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