I've seen this reported a couple of times before but the problem still persists. This is related to having no initial slash of the paths.

Sample snippet to reproduce:

Handlers.routing()
  .add(HttpString.GET, "code/\{code\}", new FetchHandler())
  .add(HttpString.POST, "code/\{code\}", new CreateHandler());

Note: there's a bug on issues.redhat.com and i cannot embed curly parentheses so I have to add a backslash. The actual code doesn't include it of course.

This produces an error on start:

Exception in thread "main" java.lang.IllegalStateException: UT000071: Cannot add path template /code/{code}, matcher already contains an equivalent pattern /code/{code}
	at io.undertow.util.PathTemplateMatcher.add(PathTemplateMatcher.java:110)
	at io.undertow.util.PathTemplateMatcher.add(PathTemplateMatcher.java:151)
	at io.undertow.server.RoutingHandler.add(RoutingHandler.java:129)
	[redacted]

I'm using the latest and greatest version: 2.0.30-Final.