Sorry to hear you’re facing problems 
If you’re urgently looking for support to keep your business running, consider checking out our paid support options.
In order to help you as quickly as possible, before clicking Create Topic please provide as much of the following as you can (you can cut and paste this into your topic):
Nextcloud version 12 Beta 4:
Operating system and version Ubuntu 16.04:
Apache or nginx version (eg, Apache 2.4.25):
PHP version (eg, 5.6):
Is this the first time you’ve seen this error?:
Yes
Can you reliably replicate it? (If so, please outline steps):
yes
The issue you are facing:
When updating from the updater App it fails on the first step:
Check for expected files
The following extra files have been found:
autotest-checkers.sh
The output of your Nextcloud log in Admin > Logging:
The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):
The output of your Apache/nginx/system log in /var/log/____:
Remember, this information may be requested if it isn’t supplied; for fastest response please provide as much as you can 
Feel free to use a pastebin service, otherwise log files can be indented with 4 spaces on each line to present them in a friendlier way on the forum.