Hi, I cannot login with any user ADMIN or normal user after nextcloud 20 → 21 upgrade.
I was initially able to login to existing accounts , but one by one we were locked out of the accounts.
files are stored on S3 object storage and users where created after the install.
I will log in and download the nextcloud logs now.
Thank Ben
Support intro
Sorry to hear you’re facing problems 
help.nextcloud.com is for home/non-enterprise users. If you’re running a business, paid support can be accessed via portal.nextcloud.com where we can ensure your business keeps running smoothly.
In order to help you as quickly as possible, before clicking Create Topic please provide as much of the below as you can. Feel free to use a pastebin service for logs, otherwise either indent short log examples with four spaces:
example
Or for longer, use three backticks above and below the code snippet:
longer
example
here
Some or all of the below information will be requested if it isn’t supplied; for fastest response please provide as much as you can 
Nextcloud version = 21.0.1
Operating system= Ubuntu 20.04
Apache latest stable
PHP version 7.4
The issue you are facing:
Is this the first time you’ve seen this error? (Y/N):
Steps to replicate it:
The output of your Nextcloud log in Admin > Logging:
[no app in context] Warning: Login failed: xxxxx (Remote IP: x.x.x.x)
POST /index.php/login
from x.x.x.x at 2021-04-13T02:39:00+00:00
The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):
PASTE HERE
The output of your Apache/nginx/system log in /var/log/____:
PASTE HERE