Looks like pretty much this same issue: https://issues.jenkins-ci.org/browse/JENKINS-29805
Also on SO: https://stackoverflow.com/questions/58139761/pipeline-maven-plugin-not-replacing-servers-in-global-settings-xml-from-jenkin
hard coding "<servers></servers>" in the config file works but configuring "Server Credentials" from jenkins credentials is not working. I tried with and without "Replace all"