See e.g. https://github.com/datalad/datalad-extensions/runs/698281348 where it just says that the last step (Run datalad tests) has failed and took over 58m to complete. My guess it stalled and may be flooded outputs at some point. No longs available online or in the download bundle (present for other matrix runs).
When the runner machine runs out of disk, the runner will crash. I am not sure whether this is the cause of your scenario, I am trying to involve some senior engineers to investigate your issue. You patience will be appreciated.