slf4j binding uses the class loader to find it's binding. If the logging fraction is present the binding should be org.jboss.logmanager:slf4j-jboss-logmanager which is present the modules directory of the archive. However if the the module requesting the binding is located in the m2repo/org/wildfly/swarm/*-modules path it likely only has the org.slf4j module dependency and for some reason the paths don't include the binding.
The logging-modules.jar does seem to include the correct module.xml so I'm not sure how the resolution of modules works. Maybe there is an issue because the org.slf4j and org.slf4j.impl dependencies are circular dependencies.