Why do I get alerts for "Increase in DMARC-SPF alignment failures" when my messages are still passing DMARC?

Infrastructure Alert - Increase in authentication errors from your infrastructure for domain.com

The Increase in DMARC-SPF alignment failures alert is non-actionable. It was triggered by a campaign being sent out from Mailchimp that was higher than the daily average. The messages did pass DMARC via DKIM but the alert was triggered because DMARC-SPF authentication failed. This is expected behavior for Mailchimp as they do not support DMARC-SPF so you may get this alert on an infrequent basis.