Client connection refused

Processing Electronics (Arduino, etc.)
1

hello guys, hope you doing all well, so i i have a bunch of arduinos connected to local network via ethernet, a user can than interact with them via GUI done by processing, after testing with three arduinos everything works fine, but when i further increase the number to 4 , i m getting this error contiounsly on one of the arduinos :

java.net.ConnectException: Connection refused: connect
i can t   reach it 
	at java.base/sun.nio.ch.Net.connect0(Native Method)
	at java.base/sun.nio.ch.Net.connect(Net.java:579)
	at java.base/sun.nio.ch.Net.connect(Net.java:568)
	at java.base/sun.nio.ch.NioSocketImpl.connect(NioSocketImpl.java:593)
	at java.base/java.net.SocksSocketImpl.connect(SocksSocketImpl.java:327)
	at java.base/java.net.Socket.connect(Socket.java:633)
	at java.base/java.net.Socket.connect(Socket.java:583)
	at java.base/java.net.Socket.<init>(Socket.java:507)
	at java.base/java.net.Socket.<init>(Socket.java:287)
	at processing.net.Client.<init>(Unknown Source)
	at G4P_interface.automatique_window_draw(G4P_interface.java:1335)
	at jdk.internal.reflect.GeneratedMethodAccessor6.invoke(Unknown Source)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:568)
	at g4p_controls.GWindow.draw(Unknown Source)
	at g4p_controls.GWindowAWT.draw(Unknown Source)
	at processing.core.PApplet.handleDraw(PApplet.java:2094)
	at processing.awt.PSurfaceAWT$9.callDraw(PSurfaceAWT.java:1386)
	at processing.core.PSurfaceNone$AnimationThread.run(PSurfaceNone.java:356)

when i send to all 4 , one of them always refuse the connection ( it still goes through sometimes), i checked the ip adresses they are all corrects, tried to increase connection timeout, retry with delay but still it persist, any leads ? i want to know also why does this exception occur ? i did nt find the documentation about this exception.