We analyzed the issue in a support case. The problem in that specific case was, that the wrong mysql-server package version was installed. We currently have an issue where the mysql-server package for UCS 4.1 errata is newer than in UCS 4.2.
To get the currently installed version, the output of e.g. apt-cache policy mysql-server should be checked. If the installed package on your UCS 4.2 system is not from a UCS 4.2 repository, the mysql-server daemon init script will not wait long enough for the mysql process to start up.
An updated mysql-server erratum for UCS 4.2-1 will be relased soon. In the meantime, apt-get install mysql-server=5.5.54-0.A~4.2.0.201703071716 mysql-server-5.5=5.5.54-0.A~4.2.0.201703071716 will install the correct mysql-server version for UCS 4.2