I tested that recently. That job instance was recorded as failed in the dashboard and listed the exception which indicated that the timeout had expired while waiting for an exclusive lock.
You’ll see the following exception:
Hangfire.Storage.DistributedLockTimeoutException: Timeout expired. The timeout elapsed prior to obtaining a distributed lock on the 'xxx' resource.
at Hangfire.SqlServer.SqlServerDistributedLock.Acquire(IDbConnection connection, String resource, TimeSpan timeout)