Class BufferPoolMXBeanResource transforms the name of retrieved MXBeans to handle embedded spaces and other special characters by calling method escapeMBeanName. Later on class BufferPoolMXBeanResourceAttributeHandler uses the name to identify the corresponding bean. Unfortunately, when BufferPoolMXBeanResourceAttributeHandler checks that the bean is registered it does not reverse the transformation by calling unescapeMBeanName.
This causes a lookup failure when the new buffer pool non-volatiel memory MXBean is encountered on JDK14. Although Wildlfy appears to continue running the error message appears to cause failures in some of the Wildfly tests, notably those that check error stream output.
See the referenced forum thread for full details.