GitLab 18 fails to execute scheduled pipelines when timezone is used in the cron syntax

We recently upgraded our self-hosted premium server from GitLab v17 to v18. This revealed an interesting regression with scheduled pipelines where many projects which had worked for years no longer execute. When looking at the schedule, the active flag is set but the scheduled pipeline page lists them as inactive:

Terraform confirmed that nothing changed from the API-standpoint from where our configuration has been for years. What's also interesting is that if you attempt to save the page you get an incorrect validation error stating that a cron expression like 11 14 * * 0 is invalid.