mirror probe failed without any explanation in logs

This morning I received an email alert from launchpad indicating my releases mirror at mirror.steadfastnet.com/releases/ was dropped because it failed the probe test. The mirror in question is:

https://launchpad.net/ubuntu/+mirror/mirror.steadfast.net-release

The log file referenced at the time was:

http://launchpadlibrarian.net/464354768/mirror.steadfast.net-release-probe-logfile.txt

This log file indicates no errors (this is the whole thing):

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Mon Feb 10 09:23:43 2020: Found all ISO images for series The Bionic Beaver and flavour ubuntu.
Mon Feb 10 09:23:43 2020: Found all ISO images for series The Eoan Ermine and flavour ubuntu.
Mon Feb 10 09:23:43 2020: Found all ISO images for series The Precise Pangolin and flavour ubuntu.
Mon Feb 10 09:23:43 2020: Found all ISO images for series The Trusty Tahr and flavour ubuntu.
Mon Feb 10 09:23:43 2020: Found all ISO images for series The Xenial Xerus and flavour ubuntu.
-

Upon deeper inspection, I was able to determine that my mirror was missing all of the Disco release. Based on discussion with fo0bar and hloeung in #ubuntu-mirrors it appears that Disco was intended to be removed today, though one of the rsync pool servers continued to have it.

Assuming that Disco missing was the fault, there is no indication that's the case. If it was not the fault, there is still no clue as to why the mirror was failed. It's possible the root cause was effectively a race condition due to the timing of the Disco removals.

The bug I'm reporting is that launchpad should certainly provide some indication why the mirror was failed in the log files if it's going to be failed out.