LetsEncrypt failure after rebuild

I just had to rebuild my NCP set up on my Pi (docker container running under HypriotOS) and since then I’m having an issue with Lets Encrypt. It’s a fresh install now, with a newly downloaded image and all the old data folder removed.

Before the rebuild it was working ok, but if I run it now I get an error - see the last line on the tail of the log:

File "/usr/lib/python2.7/dist-packages/certbot/main.py", line 626, in obtain_cert
    action, _ = _auth_from_available(le_client, config, domains, certname, lineage)
  File "/usr/lib/python2.7/dist-packages/certbot/main.py", line 107, in _auth_from_available
    lineage = le_client.obtain_and_enroll_certificate(domains, certname)
  File "/usr/lib/python2.7/dist-packages/certbot/client.py", line 309, in obtain_and_enroll_certificate
  File "/usr/lib/python2.7/dist-packages/certbot/storage.py", line 967, in new_lineage
    with open(target["cert"], "wb") as f:
IOError: [Errno 2] No such file or directory: u'/etc/letsencrypt/live/darrenhill.spdns.eu-0002/cert.pem'

The cert.pem file exists, so I’m presuming there’s a typo somewhere in the script that’s introducing the rogue “u” at the start of the line (the above is copy/paste from the log).

Can someone help with what to change or where to go from here to get it working again?

NextCloudPi version v0.59.8
NextCloudPi image NextCloudPi_06-20-18
distribution Debian GNU/Linux 9 \n \l