Sync does NOT support folders/files without extension containing asterisks (*) at the end of the folder/file name.
Test* - invalid file/folder name
Test - valid file/folder name
Test*.txt - valid folder name
Te*st - valid file/folder name
In case an invalid folder/file name is picked, Sync may interpret it as a piece of system data, which, in turn, may lead to program errors and/or disruption of syncing.