Error with base.php not detected

[thennicke]

I've followed your tutorial as meticulously as I can but I can't open the web GUI. Here are the last few lines of the log up until the error:

nextcloud     | Initializing nextcloud 30.0.6.2 (this can take a while) ...
nextcloud     | Setting permissions
nextcloud     | New nextcloud instance
nextcloud     | Please run the web-based installer on first connect!
nextcloud     | Initializing finished
nextcloud     | After completing the web-based installer, restart the Nextcloud container to apply default memory caching and transactional file locking configurations.
nextcloud     | Alternatively, you can apply your own configurations by editing /config/www/nextcloud/config/config.php following the documentation:
nextcloud     | https://docs.nextcloud.com/server/latest/admin_manual/configuration_server/caching_configuration.html
nextcloud     | https://docs.nextcloud.com/server/latest/admin_manual/configuration_files/files_locking_transactional.html
nextcloud     | [custom-init] No custom files found, skipping...
nextcloud     | [ls.io-init] done.
nextcloud     | Exception: Not installed in /app/www/public/lib/base.php:223
nextcloud     | Stack trace:
nextcloud     | #0 /app/www/public/lib/base.php(668): OC::checkInstalled()
nextcloud     | #1 /app/www/public/lib/base.php(1134): OC::init()
nextcloud     | #2 /app/www/public/cron.php(24): require_once('...')
nextcloud     | #3 {main}

The last five lines here then repeat over and over again, once every five minutes (I guess because of cron).

It's pretty similar to this issue (probably permissions related).
Any advice on how to approach this problem? Thanks