Why did ubuntu2004-large fail to allocate sufficient hosts?

https://mongodb.splunkcloud.com/en-US/app/search/burst_stats?form.distro=ubuntu2004-large&form.time.earliest=1637643600&form.time.latest=1637730000&form.index_source_token=evergreen

This blocked a user's patch build for seemingly no reason, before spontaneously resolving around 9:45 eastern.
https://mongodb.slack.com/archives/C0V896UV8/p1637678020110500