The tests for the Page grade hang on the following test:
"Test page grade: Test events and timing — at sequence position 8 of 24"
as well as
"Test page grade: Test events and timing — at sequence position 13 of 24"
The particular event being waited on in both cases is "uio.prefsEditorLoader.messageLoader.events.onResourcesLoaded" after a language change. In this part of the sequence, there are two event listeners back to back, so it could be related to that, or it could simply be that the event immediately prior to it (menu.events.onControlsBound, to wait for that UI to finish rendering) is firing sometimes before and sometimes after UIO's onResourcesLoaded.
This issue doesn't always occur, and seems to be more frequent depending on the exact environment and browser. In Edge 44, it happens over 90% of the time, while in Firefox 78 it's more like 30%, and in Chrome 83 it seems to happen less than 10% of the time. This also only seems to occur when running the browser tests from the server hosting rather than hosting locally.