I was hoping PeterT would get here first, but my name has been invoked
The first thing to check is that the driver configuration is still correct. There isn't any reason to think it will have changed, but it is a good idea to check.
Then check that the books in the calibre library do have the shelves set as you expect. Is the column you are using one you edit, or are you using a column based on a template?
Then connect the ereader again, but, could you do it in a debug session? This will grab the log and I can have a look at it if the shelves aren't fixed. Do this by starting calibre without the device connected. Then right click on the preferences button and select "Restart in debug mode". Calibre will close and reopen and display a message about the log file. Dismiss the message and connect the device. When calibre has finished its initial sync, eject the device and close calibre. When it closes, it will display the debug log. If the shelves haven't been fixed, post the log or PM it to me.