Sounds like a limitation of the WD sync software, which is probably getting it from win32api.
Windows has a max path length of 260 characters.
Linux has a max path of 4096 characters. (mentioned because the MyCloud is a linux box underneath.)
according to MS, there IS a way to get very long paths, but I dont know if the wdsync utility supports this file access convention.
the pertinent part is this:
Note File I/O functions in the Windows API convert "/" to "\" as part of
converting the name to an NT-style name, except when using the
"\\?\" prefix as detailed in the following sections.
The Windows API has many functions that also have Unicode versions
to permit an extended-length path for a maximum total path length of
32,767 characters. This type of path is composed of components separated
by backslashes, each up to the value returned in the
lpMaximumComponentLength parameter of the GetVolumeInformation
function (this value is commonly 255 characters). To specify an
extended-length path, use the "\\?\" prefix.
For example, "\\?\D:\very long path".`
see if the WDSync utility will accept a path entered with that convention.