I'm getting something similar but a certificate expired warning from curl. No nextcloud files are installed in the webroot:
[cont-init.d] 10-adduser: exited 0.
[cont-init.d] 20-config: executing...
[cont-init.d] 20-config: exited 0.
[cont-init.d] 30-keygen: executing...
generating self-signed keys in /config/keys, you can replace these with your own keys if required
Generating a 2048 bit RSA private key
.................+++
.+++
writing new private key to '/config/keys/cert.key'
-----
[cont-init.d] 30-keygen: exited 0.
[cont-init.d] 40-config: executing...
[cont-init.d] 40-config: exited 0.
[cont-init.d] 50-install: executing...
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
curl: (60) SSL certificate problem: certificate has expired
More details here: https://curl.haxx.se/docs/sslcerts.html
curl failed to verify the legitimacy of the server and therefore could not
establish a secure connection to it. To learn more about this situation and
how to fix it, please visit the web page mentioned above.
tar: /tmp/nextcloud.tar.bz2: Cannot open: No such file or directory
tar: Error is not recoverable: exiting now
[cont-init.d] 50-install: exited 0.
[cont-init.d] 60-memcache: executing...
cp: cannot create regular file '/config/www/nextcloud/config/config.php': No such file or directory
chown: cannot access '/config/www/nextcloud/config/config.php': No such file or directory
[cont-init.d] 60-memcache: exited 1.
[cont-init.d] done.
[services.d] starting services
[services.d] done.
Could not open input file: /config/www/nextcloud/cron.php
Guess I'll try again later and maybe they'll update their cert.