JENKINS-43495 and JENKINS-43629 users are encountering that their Jenkins breaks if they install Jenkins 2.54 via apt (pkg.jenkins.io). This is caused by a missing dependency to Java 8 on the package.
The issue was resolved for the Jenkins 2.55 package by adding the Java 8 dependency. But because the 2.54 package is still present on pkg.jenkins.io without a dependency to Java 8 systems that do not have the option to install Java 8 will automatically install Jenkins up to 2.54, breaking their Jenkins installation.
A good example of this is Ubuntu 14.04 which has no official support for Java 8. Installing Jenkins on these systems will result in 2.54 being installed.
To resolve the issue please remove the Jenkins 2.54 package from pkg.jenkins.io and/or update the 2.54 package to add the Java 8 requirement.