My server occasionally issues such an error, which tells me to lower the maxLifetime value. Although I have set it to 30000, it still issues such a prompt. When I lower the value to a lower value, it will revert to 180000. Is this a loophole or my problem?

[15:01:08 WARN]: [Craft Scheduler Thread - 19] WARN com.zaxxer.hikari.pool.r - HikariPool-1 - Failed to validate connection com.mysql.jdbc.JDBC4Connection@7fde312 (No operations allowed after connection closed.). Possibly consider using a shorter maxLifetime value.
[15:01:08 WARN]: [Craft Scheduler Thread - 19] WARN com.zaxxer.hikari.pool.r - HikariPool-1 - Failed to validate connection com.mysql.jdbc.JDBC4Connection@38052008 (No operations allowed after connection closed.). Possibly consider using a shorter maxLifetime value.
[15:01:08 WARN]: [Craft Scheduler Thread - 19] WARN com.zaxxer.hikari.pool.r - HikariPool-1 - Failed to validate connection com.mysql.jdbc.JDBC4Connection@5008b169 (No operations allowed after connection closed.). Possibly consider using a shorter maxLifetime value.
[15:01:08 WARN]: [Craft Scheduler Thread - 19] WARN com.zaxxer.hikari.pool.r - HikariPool-1 - Failed to validate connection com.mysql.jdbc.JDBC4Connection@5863411d (No operations allowed after connection closed.). Possibly consider using a shorter maxLifetime value.
[15:01:08 WARN]: [Craft Scheduler Thread - 19] WARN com.zaxxer.hikari.pool.r - HikariPool-1 - Failed to validate connection com.mysql.jdbc.JDBC4Connection@3cddff95 (No operations allowed after connection closed.). Possibly consider using a shorter maxLifetime value.
[15:01:08 WARN]: [Craft Scheduler Thread - 19] WARN com.zaxxer.hikari.pool.r - HikariPool-1 - Failed to validate connection com.mysql.jdbc.JDBC4Connection@2dc99d66 (No operations allowed after connection closed.). Possibly consider using a shorter maxLifetime value.
[15:01:08 WARN]: [Craft Scheduler Thread - 19] WARN com.zaxxer.hikari.pool.r - HikariPool-1 - Failed to validate connection com.mysql.jdbc.JDBC4Connection@38dfe24f (No operations allowed after connection closed.). Possibly consider using a shorter maxLifetime value.
[15:01:08 WARN]: [Craft Scheduler Thread - 19] WARN com.zaxxer.hikari.pool.r - HikariPool-1 - Failed to validate connection com.mysql.jdbc.JDBC4Connection@29844e6c (No operations allowed after connection closed.). Possibly consider using a shorter maxLifetime value.
[15:01:08 WARN]: [Craft Scheduler Thread - 19] WARN com.zaxxer.hikari.pool.r - HikariPool-1 - Failed to validate connection com.mysql.jdbc.JDBC4Connection@48c7d497 (No operations allowed after connection closed.). Possibly consider using a shorter maxLifetime value.
[15:01:08 WARN]: [Craft Scheduler Thread - 19] WARN com.zaxxer.hikari.pool.r - HikariPool-1 - Failed to validate connection com.mysql.jdbc.JDBC4Connection@f4d9a5a (No operations allowed after connection closed.). Possibly consider using a shorter maxLifetime value.

When I restart the server after setting it below 30 seconds, he will automatically reply for 180 seconds

So you set it in LP?
You shoulslower it in LP and make sure it's around 30 seconds lower.

Remember that the time for wait_timeout in your database is in seconds while it is in milliseconds for LP

Even if I update the latest version of the plugin, this problem still occurs

[12:24:06 WARN]: [Craft Scheduler Thread - 38] WARN com.zaxxer.hikari.pool.r - HikariPool-1 - Failed to validate connection com.mysql.jdbc.JDBC4Connection@1ed8335e (No operations allowed after connection closed.). Possibly consider using a shorter maxLifetime value.
[12:24:06 WARN]: [Craft Scheduler Thread - 38] WARN com.zaxxer.hikari.pool.r - HikariPool-1 - Failed to validate connection com.mysql.jdbc.JDBC4Connection@9dbc57f (No operations allowed after connection closed.). Possibly consider using a shorter maxLifetime value.
[12:24:06 WARN]: [Craft Scheduler Thread - 38] WARN com.zaxxer.hikari.pool.r - HikariPool-1 - Failed to validate connection com.mysql.jdbc.JDBC4Connection@772ba074 (No operations allowed after connection closed.). Possibly consider using a shorter maxLifetime value.
[12:24:06 WARN]: [Craft Scheduler Thread - 38] WARN com.zaxxer.hikari.pool.r - HikariPool-1 - Failed to validate connection com.mysql.jdbc.JDBC4Connection@28b62f0c (No operations allowed after connection closed.). Possibly consider using a shorter maxLifetime value.
[12:24:06 WARN]: [Craft Scheduler Thread - 38] WARN com.zaxxer.hikari.pool.r - HikariPool-1 - Failed to validate connection com.mysql.jdbc.JDBC4Connection@7b4d232c (No operations allowed after connection closed.). Possibly consider using a shorter maxLifetime value.
[12:24:06 WARN]: [Craft Scheduler Thread - 38] WARN com.zaxxer.hikari.pool.r - HikariPool-1 - Failed to validate connection com.mysql.jdbc.JDBC4Connection@2c6ae107 (No operations allowed after connection closed.). Possibly consider using a shorter maxLifetime value.
[12:24:06 WARN]: [Craft Scheduler Thread - 38] WARN com.zaxxer.hikari.pool.r - HikariPool-1 - Failed to validate connection com.mysql.jdbc.JDBC4Connection@668dcfe (No operations allowed after connection closed.). Possibly consider using a shorter maxLifetime value.
[12:24:06 WARN]: [Craft Scheduler Thread - 38] WARN com.zaxxer.hikari.pool.r - HikariPool-1 - Failed to validate connection com.mysql.jdbc.JDBC4Connection@1fbf4d70 (No operations allowed after connection closed.). Possibly consider using a shorter maxLifetime value.
[12:24:06 WARN]: [Craft Scheduler Thread - 38] WARN com.zaxxer.hikari.pool.r - HikariPool-1 - Failed to validate connection com.mysql.jdbc.JDBC4Connection@df949e8 (No operations allowed after connection closed.). Possibly consider using a shorter maxLifetime value.
[12:24:06 WARN]: [Craft Scheduler Thread - 38] WARN com.zaxxer.hikari.pool.r - HikariPool-1 - Failed to validate connection com.mysql.jdbc.JDBC4Connection@7660e389 (No operations allowed after connection closed.). Possibly consider using a shorter maxLifetime value.

When I set the value below 30000 it will automatically restore ...

[13:08:17 WARN]: [me.lucko.luckperms.lib.hikari.HikariConfig] luckperms-hikari - maxLifetime is less than 30000ms, setting to default 1800000ms.

is what i say, they need to remove that min value, or just remove it so we can make it lower than 30000

I think they should remove the minimum value

same problem here, most minecraft hosting´s has the wait_timeout in exactly 30 sec, could you please make a new update so we can lower the maxlifetime ? or maybe just remove the "max min lifetime" setting and leave it without restrictions of a min value ?

That's an hikari thing, not a LP thing, there is pretty much 0 reason to have a connection lifetime less than 30 seconds, that somewhat defeats the whole purpose of pooling connections and just creates more work for the client (LP) and the server itself.

I'd suggest looking at what the actual connection timeouts are on the mysql server, and speaking to your hosting provider if you're seeing this often, that generally means that something is closing the connection in an unexpected way, or their server is not configured in a way that's "nice".

I asked the hosting service provider and he told me that connecting to Mysql is an internal network, it should not be a problem with their server, and I tried to update my mysql version, but I still get a warning.

If the MySQL server is timing out connections after less than 30 seconds, then it is definitely a problem at their end.