Hello,
The Server Send an "end" message after client(javascript api) successfully connected to server so the connection disconnected.
it doesn't happen every time,
and also I find the following line in the server's log:
Unexpected error while managing data for session Sc5b0f27563b49eecM87aT5148650:
java.lang.ClassCastException: java.base/java.lang.String cannot be cast to com.lightstreamer.d.c.v
at com.lightstreamer.k.ai.a(ai.java)
at com.lightstreamer.l.c.r.a(r.java)
at com.lightstreamer.l.c.j.a(j.java)
at com.lightstreamer.l.z.b(z.java)
at com.lightstreamer.l.a.bk.a(bk.java)
at com.lightstreamer.l.a.aq.a(aq.java)
at com.lightstreamer.l.a.aq.a(aq.java)
at com.lightstreamer.l.a.ac.a(ac.java)
at com.lightstreamer.l.r.l(r.java)
at com.lightstreamer.l.r.f(r.java)
at com.lightstreamer.l.e.a(e.java)
at com.lightstreamer.d.j.d(j.java)
at com.lightstreamer.d.b.d.b(d.java)
at com.lightstreamer.d.b.d.run(d.java)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker( ThreadPoolExecutor.java:1135)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run (ThreadPoolExecutor.java:635)
at com.lightstreamer.d.b.bt.d(bt.java)
at com.lightstreamer.d.b.bu.d(bu.java)
at com.lightstreamer.d.b.br.run(br.java)
10-Nov-18 11:51:52,150|ERROR|L.scheduler |PUMP POOLED THREAD 62 |Unexpected error while sending data: Caught: java.lang.ClassCastException: java.base/java.lang.String cannot be cast to com.lightstreamer.d.c.v.
10-Nov-18 11:51:52,150|ERROR|L.connections |PUMP POOLED THREAD 62 |Interruption during data processing: Caught: java.lang.ClassCastException: java.base/java.lang.String cannot be cast to com.lightstreamer.d.c.v.
10-Nov-18 11:51:52,166|INFO |L.requests |PUMP POOLED THREAD 49 |Closed session Sc5b0f27563b49eecM87aT5148650 with internal cause code: 43/4 (Failure).

Thanks in advance.