It consistently fails on the first directory in a long-path UNC notation server-folder.

>>> os.makedirs(r"\\?\UNC\DiskStation\already_exists", exist_ok=True)
Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "C:\Users\safihre\AppData\Local\Programs\Python\Python38\lib\os.py", line 213, in makedirs
    makedirs(head, exist_ok=exist_ok)
  File "C:\Users\safihre\AppData\Local\Programs\Python\Python38\lib\os.py", line 213, in makedirs
    makedirs(head, exist_ok=exist_ok)
  File "C:\Users\safihre\AppData\Local\Programs\Python\Python38\lib\os.py", line 223, in makedirs
    mkdir(name, mode)
OSError: [WinError 123] The filename, directory name, or volume label syntax is incorrect: '\\\\?\\UNC\\'

>>> os.makedirs(r"\\?\UNC\DiskStation\already_exists")
Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "C:\Users\safihre\AppData\Local\Programs\Python\Python38\lib\os.py", line 213, in makedirs
    makedirs(head, exist_ok=exist_ok)
  File "C:\Users\safihre\AppData\Local\Programs\Python\Python38\lib\os.py", line 213, in makedirs
    makedirs(head, exist_ok=exist_ok)
  File "C:\Users\safihre\AppData\Local\Programs\Python\Python38\lib\os.py", line 223, in makedirs
    mkdir(name, mode)
OSError: [WinError 123] The filename, directory name, or volume label syntax is incorrect: '\\\\?\\UNC\\'


The second level directory is working correctly as expected:

>>> os.makedirs(r"\\?\UNC\DiskStation\already_exists\new")

>>> os.makedirs(r"\\?\UNC\DiskStation\already_exists\new")
Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "C:\Users\safihre\AppData\Local\Programs\Python\Python38\lib\os.py", line 223, in makedirs
    mkdir(name, mode)
FileExistsError: [WinError 183] Cannot create a file when that file already exists: '\\\\?\\UNC\\DiskStation\\test_get2\\test2'


Inspecting the code, I think the problem is in the os.path.exists function that is called from within os.makedirs, the line in os.makedirs says:
if head and tail and not path.exists(head):

But:
>>> head, tail = path.split(r"\\?\UNC\DiskStation\already_exists")
('\\\\?\\UNC\\DiskStation', 'already_exists')

>>> os.path.exists(r'\\?\UNC\DiskStation')
False
>>> os.path.exists(r'\\DiskStation')
False

So it wrongly goes ahead and tries to create \\?\UNC\DiskStation

This behavior is due to issue 37609, i.e. ntpath.splitdrive fails for "UNC" device paths.

    >>> ntpath.splitdrive('//?/UNC/server/share')
    ('//?/UNC', '/server/share')

The result should be "//?/UNC/server/share". A path on the "UNC" device requires a share component, on which is mounted a local or remote filesystem directory. It's functionally part of the 'drive' path. Using just the root path or a server path on the "UNC" device is malformed in the context of a normal file API open. The former fails as ERROR_INVALID_NAME (123), and the latter fails as ERROR_BAD_PATHNAME (161). 

The incorrect splitdrive result in turn makes ntpath.split misbehave:

    >>> ntpath.split('//?/UNC/server/share')
    ('//?/UNC/server', 'share')
    >>> ntpath.split('//?/UNC/server')
    ('//?/UNC/', 'server')

The correct result should be ('//?/UNC/server/share', '').