https://github.com/jenkinsci/jenkins/pull/5668 replaced a call to Date.parse with a call to DateFormat.getDateInstance().parse(), which is not equivalent. In this case, the dates being parsed are printed using Date.toString which uses a nonstandard format that causes DateFormat.getDateInstance().parse() to throw a DateParseException 100% of the time.

This caused BootFailure.loadAttempts to always return an empty list, even if there were previous boot failures. The only usage of this method in Jenkins core is to bind the previous attempt timestamps to a Groovy hook script ("boot-failure.groovy") if one exists. I am aware of one other usage of this method in non-OSS code that tracks startup times and boot failures and was affected by the bug.