Shedlock skipped runs

Question

I am using shedlock to implement a use-case of distributed locking. My app is running on 20 machines, and I want scheduler to be executed once in every 5 minutes in any 1 machine by using implicit distributed locking provided by shedlock library.

Scheduler:

    @Scheduled(cron = "0 */5 * * * *")
    @SchedulerLock(name = "executeTaskLock",
            lockAtLeastFor = "1m",
            lockAtMostFor = "4m")
    public void executeTask() throws Exception {
        LockAssert.assertLocked();

        // task executes here which completed in around (400ms - 2s)
    }

Config:

    @Bean
    public JedisPool jedisPoolForSchedulerLocking() {

        JedisPoolConfig jedisPoolConfig = new JedisPoolConfig();
        jedisPoolConfig.setMaxTotal(2);
        jedisPoolConfig.setMaxIdle(2);
        jedisPoolConfig.setMinIdle(1);
        jedisPoolConfig.setMaxWaitMillis(500);

        return new JedisPool(jedisPoolConfig, {host}, {port}, {timeout}, {port}); 
    }

    @Bean
    public LockProvider lockProvider(@Qualifier("jedisPoolForSchedulerLocking") JedisPool jedisPool) {
        return new JedisLockProvider(jedisPool, "PRD");
    }

Issue:

I am seeing sometimes scheduler is missing the runs, for instance it runs at 12:25, 12:30 and then runs at 12:45, missed 2 runs here. Actual task completes in around (400ms - 3s), thus I have setup 1m and 4m as lockAtLeastFor and lockAtMostFor. config seems correct to me.

Doesn't know what's failing here exactly. As per official docs this can run more than once(which is fine for my use-case) but should never miss the runs.

pom.xml :

        <dependency>
            <groupId>net.javacrumbs.shedlock</groupId>
            <artifactId>shedlock-spring</artifactId>
            <version>4.42.0</version>
        </dependency>

        <dependency>
            <groupId>net.javacrumbs.shedlock</groupId>
            <artifactId>shedlock-provider-redis-jedis</artifactId>
            <version>4.42.0</version>
        </dependency>

<java.version>1.8</java.version>
<spring-boot.version>2.2.1.RELEASE</spring-boot.version>