I did a look through your ncp-report log and this is the error that is telling you what the issue is, as far as I can tell.
Doctrine\DBAL\Exception: Failed to connect to the database: An exception occurred in the driver: SQLSTATE[HY000] [2002] No such file or directory in /var/www/nextcloud/lib/private/DB/Connection.php:85
According to some good folks over at Stackoverflow this is an error code indicating the databse connection is using an unsupported socket, however there are also some threads here in this forum where people have had the same issue and it has been due to a PHP version mismatch and one because the apache server started before the database connection was established, I’ll put the links below to where I found this information 
Stackoverflow 1
Stackoverflow 2
Stackoverflow 3
Stackoverflow 4
And here is from the MySQL troubleshooting guide regarding the error code [2002] (which you are getting) both in the 5.6 version and the MySQL 8 version.
MySQL Troubleshooting 5.6
Here it is stating the same thing in the MySQL v.8 Troubleshooting documentation
MySQL Troubleshooting v.8
The error (2002)
Can't connect to ...normally means that there is no MySQL server running on the system or that you are using an incorrect Unix socket file name or TCP/IP port number when trying to connect to the server. You should also check that the TCP/IP port you are using has not been blocked by a firewall or port blocking service.
The other Nextcloud forum posts about this issue
Failed to connect to NC
Failed to connect to the database
Closed GitHub issue: Failed to connect to the database
SInce you said it occured for you after an upgrade I’d recommend starting there and checking so your PHP version all match and none of them are out of sync
I hope this helps you in the right direction to the solution and to #resolve it
Edit:
Found this is in the Nextcloud admin docs just now while looking at another issue.
Nextcloud Admin Docs
SQLSTATE[HY000] [2002] No such file or directory→ There is a problem accessing your SQLite database file in your data directory (data/nextcloud.db). Please check the permissions of this folder/file or if it exists at all. If you’re using MySQL please start your database.