Sorry this took so long for me to get sorted. The level monitoring showed that the level was running correctly and I had also checked a number of times myself that the processes were running. Only this evening did I try the level for myself and find that it was indeed not working.
After a lot of poking around I found that the issue was around the default SSL protocol used by phantomjs, which was preventing the script loading the target page. I have now configured it to use a different protocol and the level is now running correctly.
Anyone who thinks they have the correct solution should add some new activity to get the script to recheck their submission.