Confluence not starting up - Johnson.java error in catalina.out logs

I’ve just upgraded a confluence instance to 6.13 and am getting this error in my catalina.out log file:

2019-10-08 13:34:21,394 ERROR [localhost-startStop-1] [ContainerBase.[Standalone].[localhost].[/confluence]] log Exception starting filter johnson
java.lang.IllegalStateException: Johnson.getConfig() was called before initialisation
at com.google.common.base.Preconditions.checkState(Preconditions.java:173)
at com.atlassian.johnson.Johnson.getConfig(Johnson.java:82)
at com.atlassian.johnson.filters.AbstractJohnsonFilter.init(AbstractJohnsonFilter.java:69)
at org.apache.catalina.core.ApplicationFilterConfig.initFilter(ApplicationFilterConfig.java:279)
at org.apache.catalina.core.ApplicationFilterConfig.getFilter(ApplicationFilterConfig.java:260)
at org.apache.catalina.core.ApplicationFilterConfig.<init>(ApplicationFilterConfig.java:105)
at org.apache.catalina.core.StandardContext.filterStart(StandardContext.java:4700)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5340)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1408)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1398)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)

Everything else seems look right, all of my config files and confluence-home directory have the correct owners and permissions.

Any help or pointers would be much appreciated.