Error update. The following extra files have been found: gs.core

Nextcloud version: 14.0.8
Operating system and version: FreeBSD 12.0-RELEASE-p13
Apache or nginx version: nginx/1.16.1
PHP version: PHP 7.2.26

The issue you are facing:

Is this the first time you’ve seen this error? (Y/N): Y

Steps to replicate it:

  1. Start update over web interface.
    Go to settings/admin/overview#
    Current version is 14.0.8.
    Update to Nextcloud 15.0.12 available. (channel: “production”)
    Following file will be downloaded automatically:

Then press “Start update” button.

The output of your Nextcloud log in Admin > Logging:

only Warning message like this:
Warning	core	Login failed: 'username' (Remote IP: '_IP_address')

In my Nextcloud root directory I find this file:
nextcloud# ls -al gs.core
-rw------- 1 www www 40923136 28 Mar. 2019 gs.core

Can anybody help me update my nextcloud installations?

I will be greatful for any help.