Same problem here
AH00526: Syntax error on line 15 of /etc/httpd/conf/plesk.conf.d/server.conf:Invalid command 'plesklog', perhaps misspelled or defined by a module not included in the server configuration.
after updating plesk to 18.0.57 you can change username from admin account.
As soon as you do this and you log in to plesk mobile again, you will no longer get the buttons below.