Polymer Web Component Tester Unable to connect to selenium

Question

I am running Polymer Web Component Tester on a simple Polymer 2.x application template and get the following output:

hook: prepare
hook: prepare:selenium
Starting Selenium server for local browsers
15:00:30.747 INFO - Selenium build info: version: '3.7.1', revision: '8a0099a'
15:00:30.747 INFO - Launching a standalone Selenium Server
2018-02-26 15:00:30.763:INFO::main: Logging initialized @246ms to org.seleniumhq.jetty9.util.log.StdErrLog
15:00:30.825 INFO - Driver class not found: com.opera.core.systems.OperaDriver
15:00:30.856 INFO - Driver provider class org.openqa.selenium.safari.SafariDriver registration is skipped:
 registration capabilities Capabilities {browserName: safari, platform: MAC, version: } does not match the current platform WIN10
15:00:30.903 INFO - Using the passthrough mode handler
2018-02-26 15:00:30.935:INFO:osjs.Server:main: jetty-9.4.5.v20170502
2018-02-26 15:00:30.966:WARN:osjs.SecurityHandler:main: ServletContext@o.s.j.s.ServletContextHandler@5fd85d{/,null,STARTING} has uncovered http methods for path: /
2018-02-26 15:00:30.966:INFO:osjsh.ContextHandler:main: Started o.s.j.s.ServletContextHandler@5fd85d{/,null,AVAILABLE}
2018-02-26 15:00:31.122:INFO:osjs.AbstractConnector:main: Started ServerConnector@1ad4e29{HTTP/1.1,[http/1.1]}{0.0.0.0:64110}

2018-02-26 15:00:31.122:INFO:osjs.Server:main: Started @602ms
15:00:31.122 INFO - Selenium Server is up and running

Error: Unable to connect to selenium

error:   cli runtime exception: Error: Unable to connect to selenium
error:   Error: Unable to connect to selenium
    at Timeout.hasStarted [as _onTimeout] (C:\Users\a0783903\AppData\Roaming\npm\node_modules\polymer-cli\node_modules\selenium-standalone\lib\check-started.js:17:10)
    at ontimeout (timers.js:475:11)
    at tryOnTimeout (timers.js:310:5)
    at Timer.listOnTimeout (timers.js:270:5)

Command entered: polymer test --verbose --skip-selenium-install

I added some logging and the specific error is 403 UncategorizedSiteWarning

The Selenium status url requested is http://localhost:64110/wd/hub/status. I can connect to this in a browser and view the status json no problem

This is on Windows 10