Robocopy Error 50 Accessing Destination Directory (Request is not supported)

I've managed to find the issue. It looks like its related to the QNAP share not being able to handle certain security folder properties/attributes of these folders. By default the COPY and DCOPY values are:

/COPY:DAT /DCOPY:DA

I assume the /E flag sets these by default.

Attributes do appear to be a problem, but in addition to that the DCOPY parameter also needs tweaking.

/COPY:DT /DCOPY:T

This then fixes the robocopy error 50 and folders that were previously throwing errors can now be written to the destination correctly along with the files within.

It is strange that this only started showing up for relatively new folders created, but it looks to be related to attributes/properties none the less. We have a mixture of Windows/macOS clients writing to the source, so it could well be specific macOS metadata behind these directories that have been throwing robocopy off.