Update to version 1.5.7 was not successful


I have a problem with the update from version 1.5.1 to version 1.5.7.
I unziped the archive that contains the MailWizz application.
I've not run any campaign when updating.
I moved application offline from Backend -> Settings -> Common.
I Uploaded the contents of “update” overrode the existing files.
Opened the link http://domain.com/backend/index.php/update
Followed the update wizard
Also, I tried to update the mailwizz through the command line (with ssh) using the proposed command from a browser.
In both cases, the update runs without errors.
I was redirected to the page http://domain.com/backend/settings/index , but when I try to change the API status from offline to online and save the changes, I get the error 500 on my browser.
If I refresh the page in the browser then I will return to the page domain.com/backend/settings/index .
If I log out then I'll go to the welcome page but when I try to log in I get an error 500
I checked permissions and owners for all directories and files.
They the same as before the update, and the same as
in recommendations for updating.
I also checked the .htaccess file and it didn't change. His permissions and owner also didn't change.
If I replace all the files with old ones, then everything will work, but then I will not have an updated version.

@twisted1919 Сould you help me to solve this problem?