How do I resolve an unnamed requirements problem during an update? I am attempting to update my Drupal 8.2 instance to Drupal 8.6.4.  I have faithfully followed the manual installations steps found here https://www.drupal.org/docs/8/update/update-core-manually.

I replace the core and vendor folders and replace all the files in the root with the 8.6.4 files.  I rename the 8.6.4 defaults.settings.php file to settings file, move my unique settings into that file and upload it to sites/default. I then visit update.php, but I get stuck at the requirements stage.

There is an error saying "Requirements Problem: Check the messages and try again."  There are, however, no messages.



I'm happy to keep troubleshooting this but I need to know where I'm going wrong.  How can I discover what the Requirements Problem(s) are?

Some Other Details


Both the database and the Drupal server are running in a AWS VPC.
The server is a linux machine: VERSION="16.04.5 LTS (Xenial Xerus)
Drush is not working or installed. The original sysadmin didn't install it as part of the Drupal installation and I haven't added it since.
Composer is installed but I've never used it to manage Drupal versions or dependencies.
Drupal is behind an nginx reverse-proxy.  I have the made allowances for Drupal in the nginx conf file as recommended here: https://www.nginx.com/resources/wiki/start/topics/recipes/drupal/.  Mostly just this rule  location ~ '\.php$|^/update.php' {...}
There are other non-Drupal tables in the same DB that Drupal uses.
Drupal tables are prefixed: drupal_
We use drupal in a headlessly.  A separate Node.js app interacts with Drupal via Drupal Rest routes and is also connected to the same DB as Drupal.


Issues I've already resolved


Missing sourcecode for hello_world module. Removed hello_world from Drupal table: drupal_key_value
$settings['update_free_access'] = TRUE;


Things I've tried:


checking the apache2 error logs. No errors thrown.
checking the apache2 access logs. Just shows access to update.php


Let me know if I should post any more information.  Also, if using drush or composer would help, I'm interested in getting those going on my site anyway, and would be happy to install them.  In summary, during a Drupal 8 upgrade, Drupal complains about Requirement Problems but never lists them. How can I discover what the Requirements Problem(s) are?
Since the database information was transferred into a new settings.php file instead of keeping the old one, it is possible that the the custom value for the path to the synch configuration directory is not found.

Reference: Upgrading Drupal

Look for the code:

$config_directories['sync'] = 'sites\default\files\your-config-folder


in the settings.php file &amp; update it to match the address on your web server.

"This solution worked for me.
In order to find that config_gobblygook, I looked in docroot/sites/default/files and in there is a folder named config_ and then a whole bunch of letters and numbers. I copied that full name and then inserted it into line 247 of the settings.php file."

The same problem is described here with a similar solution.

Related: 


Changing the storage location of the sync directory
How do I fix this Configuration Directory sync error?


Otherwise make sure the most recent nginx.conf file for Drupal is in use, as there have been changes to that to fix the update.php issue. See:


web /update.php sequence does not work with Drupal 8
Drupal 8 Nginx configuration on Homestead (update.php works ok)
Latest Version - NGINX