Hmm - I have solved this with your hint of it being the webroot, but I’m not entirely sure of the root cause.
It was certainly using the correct directory from the config file, but the server was indeed getting no hits in the log. In the config file, it was specified in a way that I couldn’t find any documentation of?
[[webroot_map]]
wofiel.com = /path/to/webroot/
I ended up using the same details with certonly: certbot-auto certonly -w /path/to/webroot/ -d wofiel.com which authenticated correctly. Now I have a new line in my conf with webroot_path = /path/to/webroot, (comma included) which was not previously there. Doing a --dry-run of renew also now appears to work.
Edit: Some more digging with that information shows that you helped someone else with almost the same issue over a year ago: Help us test renewal with "letsencrypt renew"
Greatly appreciated your help on this, got it solved just in the nick of time! 
Thanks,
Matt