It shouldn't be doing that.
Did you use a Mac in the process which dumps extraneous garbage on the end of each record transferred ?. That's where CleanMydrive run on the SD card removes that.
Did you shift to the 1810 maps.
Failing that what was the release of the original maps. A photo of the card and back box where it gives the serial number or a photo of the screen before you started. Then we rummage for the version that you had online to find the overall.nds file exact in case of an incompatibility but this hasn't occurred yet.
People in the past have got confused about files and directories so copy over more than the overall.nds file into that location.
Id shift to 1810 if you haven't. Download and repeat. Then work thru the steps above. Photo of card, back box etc to get to the actual.
Afraid these are the issues if you loose the overall.nds file combined with the first time of doing it. You could try the Skoda link I have you in the
resource section. That's V4 of the release. Get that working in the unit, then do the workaround update to 1810. You must observe the Mac rules if a Mac. Keka and CleanMydrive.... sorry to go on about that one.
VW instructions on the MAC
Unzipping map material
ATTENTION
If the map update is performed using the Apple® OS X operating system you may find that
(The unit) does not recognise the map material or displays it incorrectly. This is due to a
lack of compatibility between the “7 zip” program and the OS-X operating system. In addition,
the OS-X operating system has a tendency to create hidden additional files on external data
media. We therefore recommend that OS X users use the “Keka” unzipping program. We also
recommend using the “CleanMyDrive” program to remove any hidden files.