Thank you so much for your swift replies!
@JammyDodger - I have increased the relevant line to 10 s, but still get the same issue now as before (it always returns with the Fatal SSL certificate.
@Ed_S I have checked the ownership of the file as you suggested, but it seems identical to yours (except the dates):
nano@nano:/var/discourse$ sudo ls -l /etc/ssl/private/ssl-cert-snakeoil.key
-rw-r----- 1 root ssl-cert 1704 jan. 11 2017 /etc/ssl/private/ssl-cert-snakeoil.key
However I had to sudo to get the command to work, so maybe I need to grant some more privileges when running the update? I’m running it as sudo ./launcher rebuild app so not sure what else I could do here.
Stephen - I will upgrade docker now and rerun everything, then report back here
Thanks for all your help!