WARNING: Duplicate resource b4459fdd-cefe-4333-9a7b-8740366c58c4. Could be

Someone know what is the cause of this problem ? How can i reproduce it? I’m using Java 8, Vaadin 7.7.9 and apache tomcat 9.0
Full Log:

WARNING: Duplicate resource 118df12c-f826-4078-bfff-32aa3280bccb. Could be caused by a dead connection not detected by your server. Replacing the old one with the fresh one
Feb 16, 2018 9:02:47 AM org.atmosphere.cpr.DefaultBroadcaster addAtmosphereResource