There are limitations to using OneDrive for Business to synchronize items.

Maximum items* for OneDrive for Business20 000Maximum items* per Sharepoint document library5 000*** Files and folders.
** You can synchronize more than one library.

Maximum size per item2 GBMaximum name length for files and foldersSharepoint Server 2013: max. 128 chars
Sharepoint Online: max. 256 chars
Folder names: max. 250 chars
Maximum combined names (files and folders, aka "path": max. 250 charsInvalid characters:\ / : * ? " < > | &hash;
spaces are not supported
files starting with a ~Invalid chars (Sharepoint Server 2013):All of the above +
{ } % ~
names starting with a .Unsupported folder  ...