The documentation for the `undertow.filter-ref.priority` for the Undertow subsystem  suggests a filter with a higher number (e.g. 2) is executed before a filter with a lower number (e.g. 1). It appears to be the opposite.
"Defines filter order. It should be set to 1 or more. A higher number instructs the server to be included earlier in the handler chain than others under the same context."
This description is taken directly from the WildFly reference model, which is incorrect.
See discussions in