Can you see Max backoff value ? I think is 3600s by default.
A task will be scheduled for retry between minBackoff and maxBackoff duration after it fails.
If maxBackoff unspecified when the queue is created, Cloud Tasks will pick the default (3600s = 60mn).
Google cloud api explorer: https://cloud.google.com/tasks/docs/reference/rest/v2/projects.locations.queues#RetryConfig.FIELDS.max_backoff