Sometimes the body catches a cold and sits sick for days or a week.
Is there an analog in software engineering?
In a distributed architecture, message queues can fill up, load balancers can lose sight of pressure, networks experience intermittent failures, leap seconds / daylight savings time / leap day, ...
When deep in a sketchy rewrite (as opposed to a controlled refactor), the code can be shaky and sick.
A simple surge in users can flood the backlog with issues and bugs, not even because of distributed computing issues, but because of the simple fact that more eyes notice more things.
Beyond the software itself, a software engineering organization can certainly catch a cold.
One or more of the individuals on the team can be literally or metaphorically sick, which can cascade through the team's effectiveness. Policies, goals, events, ... People are poor at behaving statically.
Nothing has its best day every day.