A custom Appender class inside the project fails to load on application start with this trace:
12:57:41,858 |-ERROR in ch.qos.logback.core.joran.action.AppenderAction - Could not create an Appender of type [util.logger.XXX]. ch.qos.logback.core.util.DynamicClassLoadingException: Failed to instantiate type util.logger.XXX
....
Caused by: java.lang.ClassNotFoundException: util.logger.XXX
at at java.net.URLClassLoader$1.run(URLClassLoader.java:372)
at at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
at at java.security.AccessController.doPrivileged(Native Method)
at at java.net.URLClassLoader.findClass(URLClassLoader.java:360)
at at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at at ch.qos.logback.core.util.OptionHelper.instantiateByClassNameAndParameter(OptionHelper.java:60)

This thread on StackOverflow is also referring to the same problem with a couple of workarounds, but actually none is really a solution.