If you have multiple logging implementations on the classpath, one will be picked in a non-deterministic ("random") way. You may see logging like this.
15:04:56.264 [ERROR] [system.err] SLF4J: Class path contains multiple SLF4J bindings.
15:04:56.265 [ERROR] [system.err] SLF4J: Found binding in [jar:file:/home/max/.gradle/caches/modules-2/files-2.1/org.slf4j/slf4j-log4j12/1.7.6/6953717b9850aeb26d1b8375ca07dbd9c50eca4e/slf4j-log4j12-1.7.6.jar!/org/slf4j/impl/StaticLoggerBinder.class]
15:04:56.265 [ERROR] [system.err] SLF4J: Found binding in [jar:file:/home/max/.gradle/caches/modules-2/files-2.1/ch.qos.logback/logback-classic/1.2.3/7c4f3c474fb2c041d8028740440937705ebb473a/logback-classic-1.2.3.jar!/org/slf4j/impl/StaticLoggerBinder.class]