> FWIW, I took a quick look at it and, with nothing to go on in the way of visible messages, the best guess I could come up with is that the test run step is hitting a time out and that, in that case, no status is shown. Anyone know if that is a reasonable guess?

I think it depends on the timeout. Some of my Ubuntu builds occasionally get hard-stuck on tkinter tests, so apparently it's possible for that to spoil CI. But I believe Pipelines is going to try and terminate the process "nicely" first.