Page previews CI job began failing on 7th Dec 2017 @ 14:50.
Have been failing for a few days now.
The browser test does not fail when run outside the beta cluster:
Looking at the beta cluster, page previews seems to be working correctly, but given the test page uses "Main Page" which currently returns a 500 no page preview is shown (instead of the no preview available popup). This should be fixed by T182619.