This notification indicates that there are files with names ending in characters that are illegal on Windows systems. The characters are dot (.) and space ( ). For example there may be a file named ‘Test.txt’ or ‘Test.txt’
Since the client may synchronize data to a number of devices, this may become an issue in the future if the folder is joined on a device running Windows.
When this notification appears in the client, you can select an new, safe name for the file and rename it.