Radom failure when run selenium tests in parallel with error info as 'cannot forward the request unexpected end of stream on Connection`

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Zalenium Image Version(s):
3.14.0d Docker Version:
18.06.1-ce If using docker-compose, version:
1.22.0

OS: MacOS High Sierra 10.13.6 16GB RAM

Docker Command to start Zalenium:
I use docker compose to start the service

 version: "3"
services:
    zalenium:
        image: "dosel/zalenium"
        container_name: zalenium
        hostname: zalenium
        tty: true
        volumes:
            - '/tmp/videos:/home/seluser/videos'
            - '/var/run/docker.sock:/var/run/docker.sock'
            - '/usr/local/bin/docker:/usr/local/bin/docker'
        ports:
            - 4444:4444
        command: >
          start --chromeContainers 4
                --firefoxContainers 0
                --maxDockerSeleniumContainers 6
                --maxTestSessions 200
                --screenWidth 1200 --screenHeight 900
                --timeZone "America/New_York"
                --videoRecordingEnabled false
                --sauceLabsEnabled false
                --browserStackEnabled false
                --testingBotEnabled false
                --startTunnel false
        environment:
          - HOST_UID
          - HOST_GID
          - SAUCE_USERNAME
          - SAUCE_ACCESS_KEY
          - BROWSER_STACK_USER
          - BROWSER_STACK_KEY
          - TESTINGBOT_KEY
          - TESTINGBOT_SECRET 

Expected Behavior -

The test should run without random error

Actual Behavior -

Now I am getting random test failure. It looks like the request to Selenium does not get through and yield a 500 error, this triggers the failure. I have 4 tests in parallel, and 50 test cases in total. There are about 4-5 tests will fail randomly due to this error. Here is the stacktrace of the error,

2018-10-11 13:01:31,197 root INFO Take screenshot and save as 308fe567.png
2018-10-11 13:01:31,199 selenium.webdriver.remote.remote_connection DEBUG GET http://192.168.240.2:4444/wd/hub/session/af67b690272dd60a3c34f90d2467dc1d/screenshot {"sessionId": "af67b690272dd60a3c34f90d2467dc1d"}
2018-10-11 13:01:31,202 urllib3.connectionpool DEBUG Starting new HTTP connection (1): 192.168.240.2:4444
2018-10-11 13:01:39,841 urllib3.connectionpool DEBUG http://192.168.240.2:4444 "GET /wd/hub/session/af67b690272dd60a3c34f90d2467dc1d/screenshot HTTP/1.1" 500 11436
2018-10-11 13:01:39,842 selenium.webdriver.remote.remote_connection DEBUG Finished Request
2018-10-11 13:01:39,844 root INFO Take screenshot error
2018-10-11 13:01:39,846 selenium.webdriver.remote.remote_connection DEBUG GET http://192.168.240.2:4444/wd/hub/session/af67b690272dd60a3c34f90d2467dc1d/screenshot {"sessionId": "af67b690272dd60a3c34f90d2467dc1d"}
2018-10-11 13:01:39,846 urllib3.connectionpool DEBUG Starting new HTTP connection (1): 192.168.240.2:4444
2018-10-11 13:01:43,108 urllib3.connectionpool DEBUG http://192.168.240.2:4444 "GET /wd/hub/session/af67b690272dd60a3c34f90d2467dc1d/screenshot HTTP/1.1" 500 3261
2018-10-11 13:01:43,109 selenium.webdriver.remote.remote_connection DEBUG Finished Request
2018-10-11 13:01:43,109 root ERROR An error ocurred:
Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/golem_framework-0.5.0-py3.6.egg/golem/actions.py", line 351, in verify_element_exist_by_text
    driver.get_screenshot_as_file(img_path)
  File "/usr/local/lib/python3.6/site-packages/selenium-3.14.1-py3.6.egg/selenium/webdriver/remote/webdriver.py", line 1032, in get_screenshot_as_file
    png = self.get_screenshot_as_png()
  File "/usr/local/lib/python3.6/site-packages/selenium-3.14.1-py3.6.egg/selenium/webdriver/remote/webdriver.py", line 1064, in get_screenshot_as_png
    return base64.b64decode(self.get_screenshot_as_base64().encode('ascii'))
  File "/usr/local/lib/python3.6/site-packages/selenium-3.14.1-py3.6.egg/selenium/webdriver/remote/webdriver.py", line 1074, in get_screenshot_as_base64
    return self.execute(Command.SCREENSHOT)['value']
  File "/usr/local/lib/python3.6/site-packages/selenium-3.14.1-py3.6.egg/selenium/webdriver/remote/webdriver.py", line 321, in execute
    self.error_handler.check_response(response)
  File "/usr/local/lib/python3.6/site-packages/selenium-3.14.1-py3.6.egg/selenium/webdriver/remote/errorhandler.py", line 242, in check_response
    raise exception_class(message, screen, stacktrace)

selenium.common.exceptions.WebDriverException: Message: cannot forward the request unexpected end of stream on Connection{192.168.240.6:40002, proxy=DIRECT hostAddress=/192.168.240.6:40002 cipherSuite=none protocol=http/1.1}

Stacktrace:
    at org.openqa.grid.web.servlet.handler.RequestHandler.process (RequestHandler.java:143)
    at org.openqa.grid.web.servlet.DriverServlet.process (DriverServlet.java:86)
    at org.openqa.grid.web.servlet.DriverServlet.doGet (DriverServlet.java:64)
    at javax.servlet.http.HttpServlet.service (HttpServlet.java:687)
    at javax.servlet.http.HttpServlet.service (HttpServlet.java:790)
    at org.seleniumhq.jetty9.servlet.ServletHolder.handle (ServletHolder.java:860)
    at org.seleniumhq.jetty9.servlet.ServletHandler$CachedChain.doFilter (ServletHandler.java:1650)
    at io.prometheus.client.filter.MetricsFilter.doFilter (MetricsFilter.java:170)
    at org.seleniumhq.jetty9.servlet.ServletHandler$CachedChain.doFilter (ServletHandler.java:1637)
    at org.seleniumhq.jetty9.servlet.ServletHandler.doHandle (ServletHandler.java:533)
    at org.seleniumhq.jetty9.server.handler.ScopedHandler.handle (ScopedHandler.java:143)
    at org.seleniumhq.jetty9.security.SecurityHandler.handle (SecurityHandler.java:548)
    at org.seleniumhq.jetty9.server.handler.HandlerWrapper.handle (HandlerWrapper.java:132)
    at org.seleniumhq.jetty9.server.handler.ScopedHandler.nextHandle (ScopedHandler.java:190)
    at org.seleniumhq.jetty9.server.session.SessionHandler.doHandle (SessionHandler.java:1595)
    at org.seleniumhq.jetty9.server.handler.ScopedHandler.nextHandle (ScopedHandler.java:188)
    at org.seleniumhq.jetty9.server.handler.ContextHandler.doHandle (ContextHandler.java:1253)
    at org.seleniumhq.jetty9.server.handler.ScopedHandler.nextScope (ScopedHandler.java:168)
    at org.seleniumhq.jetty9.servlet.ServletHandler.doScope (ServletHandler.java:473)
    at org.seleniumhq.jetty9.server.session.SessionHandler.doScope (SessionHandler.java:1564)
    at org.seleniumhq.jetty9.server.handler.ScopedHandler.nextScope (ScopedHandler.java:166)
    at org.seleniumhq.jetty9.server.handler.ContextHandler.doScope (ContextHandler.java:1155)
    at org.seleniumhq.jetty9.server.handler.ScopedHandler.handle (ScopedHandler.java:141)
    at org.seleniumhq.jetty9.server.handler.StatisticsHandler.handle (StatisticsHandler.java:169)
    at org.seleniumhq.jetty9.server.handler.HandlerWrapper.handle (HandlerWrapper.java:132)
    at org.seleniumhq.jetty9.server.Server.handle (Server.java:530)
    at org.seleniumhq.jetty9.server.HttpChannel.handle (HttpChannel.java:347)
    at org.seleniumhq.jetty9.server.HttpConnection.onFillable (HttpConnection.java:256)
    at org.seleniumhq.jetty9.io.AbstractConnection$ReadCallback.succeeded (AbstractConnection.java:279)
    at org.seleniumhq.jetty9.io.FillInterest.fillable (FillInterest.java:102)
    at org.seleniumhq.jetty9.io.ChannelEndPoint$2.run (ChannelEndPoint.java:124)
    at org.seleniumhq.jetty9.util.thread.strategy.EatWhatYouKill.doProduce (EatWhatYouKill.java:247)
    at org.seleniumhq.jetty9.util.thread.strategy.EatWhatYouKill.produce (EatWhatYouKill.java:140)
    at org.seleniumhq.jetty9.util.thread.strategy.EatWhatYouKill.run (EatWhatYouKill.java:131)
    at org.seleniumhq.jetty9.util.thread.ReservedThreadExecutor$ReservedThread.run (ReservedThreadExecutor.java:382)
    at org.seleniumhq.jetty9.util.thread.QueuedThreadPool.runJob (QueuedThreadPool.java:708)
    at org.seleniumhq.jetty9.util.thread.QueuedThreadPool$2.run (QueuedThreadPool.java:626)
    at java.lang.Thread.run (Thread.java:748)