Hello. This is not a known issue.
Does the client still work normally when you see this log?
Can you see if the log lines correspond to updates coming from the Server?
We must collect information by enriching the client log.
Please add the following block at the beginnig of your Lightstreamer-related code.

Code:
require(["SimpleLoggerProvider","ConsoleAppender","LightstreamerClient","LogMessages"], 
  function(SimpleLoggerProvider,ConsoleAppender,LightstreamerClient) {
    var loggerProvider = new SimpleLoggerProvider();
    LightstreamerClient.setLoggerProvider(loggerProvider);
    loggerProvider.addLoggerAppender(new ConsoleAppender("DEBUG","lightstreamer.sharing"));
    loggerProvider.addLoggerAppender(new ConsoleAppender("DEBUG","lightstreamer.subscriptions"));
});
Note that if you make many subscriptions the log may be huge. In that case, please try to set up a shorter test case.