Nextcloud suddenly in maintenance mode

I should first start by letting you know that NextCloud is installed by the Marketplace App in /var/www/nextcloud. The latest release (download.nextcloud.com/server/releases/latest.zip) is downloaded and extracted to that folder.

By default, logs are not set up, which may help you determine what's the cause behind the maintenance page. However, you can configure the logs with the help of NextCloud's documentation and a relevant post I found in Nextcloud's forum:

• Nextcloud Docs | Logging
• Nextcloud Logfile Not in /var/log/nextcloud.log

When those articles refer to config.php, that file is located in /var/www/nextcloud/config.

You apparently may also be able to straight up turn off the maintenance mode:

• This Nextcloud instance is currently in maintenance mode
• My Nextcloud went into Maintenance Mode?!?

The command those users execute (occ) has an article in Nextcloud's Docs:

Nextcloud Docs | Maintenance commands

The occ command is found in /var/www/nextcloud.