Right sorry, add "debug debugging" - the first enables kernel debug, the second enables systemd debug (and preserves the journal across boots).
After you've enabled the debugging, reboot - presumably your system will hang, so power cycle etc.
Once the system is back up, run the following:
The first command just adds an entry to the log which will make finding where you started the shutdown that bit easier.
Hopefully the system will hang on shutdown, in which case power cycle.
After the system is back up, run:
and paste the link. Thanks.