The xxx file has been ignored because it already exists as XXX, or
The xxx folder has been ignored because it already exists as XXXSyncBack is not case-sensitive for filenames or folder names, which is the same as how Windows treats filenames. For example, in a Windows folder you cannot have a file called xxx.txt and XXX.TXT. Also, if you have a file called xxx.txt then you can refer to it as Xxx.txt, XXX.txt, etc., i.e. Windows does not care what the filename case is. It will preserve the case, but for reference purposes the case is not relevant.
However, some file systems (e.g. file systems on Linux/UNIX, often encountered on NAS devices and FTP servers), are case-sensitive, meaning you can have multiple files in the same folder that have the same name and are only different in their case. If SyncBack scans a folder that has multiple files with the same filename (or folder name), which differ only in case, then it will only record one of those files/folders. The others will be ignored and an error message recorded.
Why? One major reason is that if (for example), there were two files on the non-Windows side in the same folder (etc.)
and SyncBack were to copy both files in succession to the Windows side, the second file to be copied there would overwrite the first, because Windows thinks they are the same file.