The Manifest of logback-classic does not declared the OSGi Service Loader Mediator entries to be able to consume logback.classic.spi.Configurator services provided by other bundles.

At the moment, if one provides a Configurator in another bundle this has to be workaround. For example when using Apache Aries SPI Fly by using the Dynamic Weaving by auto properties, the following VM-argument needs to be added to an application:
-Dorg.apache.aries.spifly.auto.consumers=ch.qos.logback.classic

Furthermore the OSGi Service Loader Mediator entry for the provided jakarta.servlet.ServletContainerInitializer service (implemented by 
LogbackServletContainerInitializer) is missing as well.