There could be 2 reason. first mysql server has lots of open connections so it has slowed to manage new client, so check the server status with root super privileges or process privileges like root account-
Mysql> show processlist;
+----+-------------+-------------------+------+---------+------+----------------------------------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+-------------+-------------------+------+---------+------+----------------------------------+------------------+
| 2 | system user | | NULL | Connect | 1188 | Waiting for master to send event | NULL |
| 5 | root | smart.local:39850 | NULL | Query | 0 | init | show processlist |
+----+-------------+-------------------+------+---------+------+----------------------------------+------------------+
2 rows in set (0.00 sec)
Second possiblity there could be problem with connector. The issue was also present on our side with MySql Connector .Net 6.6.5. The MySql Connector .Net 6.8.3 is solving this issue.
if both are ok then the link can be helpful.
Very slow opening MySQL connection using MySQL Connector for .net