We try to copy files from one Document Library in site A to another Document Library in site B but without the folder structure.
For this we configure a display with the "no folder" view option activated.
When we select the files (flat representation) and use the "Move to" or "Copy to" toward Document Library in site B we have an error stating that the source files are in multiple folders and cannot be transfer and that we need to copy files folder by folder.
Now if we create another Document Library not in Site B but in the same Site A and do the same operation there's no error at all and the copy works perfectly.
Then we can select files from that flat Document Library to the one in Site B with no issue.
This workaround works but makes no sense to us.
The question is then, what are the differences between two documents library that belongs to the same site vs belong to two different sites and that prevent or allow that kind of files transfert ?
Is that behavior normal or is it a bug that must be corrected ?
Is there a setting that we don't know about that will fixed the issue ?
Complete use case is to maintain a Folder structure in a team site enriched with Document Set Metadata to allow folder based sync with onedrive and when Teams Project is finished move final deliverables to a Communication site document library without any folders to rely only on taxonomy metadata defined in the source Document Library.