Mysql error:Timeout expired. But I check my mysql pool, it's not full.

[Cordium1990]

2022-05-09 13:41:37 - CharacterManager: ERROR: MySql.Data.MySqlClient.MySqlException (0x80004005): error connecting: Timeout expired. The timeout period elapsed prior to obtaining a connection from the pool. This may have occurred because all pooled connections were in use and max pool size was reached.
在 MySql.Data.MySqlClient.MySqlPool.GetConnection()
在 MySql.Data.MySqlClient.MySqlConnection.Open()
在 TShockAPI.DB.DbExt.Query(IDbConnection olddb, String query, Object[] args)
在 TShockAPI.DB.CharacterManager.InsertPlayerData(TSPlayer player, Boolean fromCommand)
My mysql version is mysql-5.7.33-winx64.
This is my mysql settings.