I first assumed this was because one of the build steps timed out. But on a second look I saw that the “collect artifacts” step at the end was actually run, but failed uploading.
Thanks for pointing this out to us! It looks like the second build you posted also timed out and uploaded its artifacts without errors, so it was probably a coincidence. I believe the artifact collection error in the first build was probably caused by intermittent network issues which we try our best to prevent, and should be rare. Regardless, please feel free to continue pointing out issues like these to us here on Discuss!