Defining a pattern layout that contains:
does not work – the filters are applied but the separator is not.
Only if the filters are removed does the separator apply to the layout.
Reproduction recipe, including config file and test program here: https://gist.github.com/rocketraman/9a92ce76ee79bf6a15ab9b3a5ec95e08
Above you can see that the exception separator was not applied – the default newlines are present in the output instead.