Connection failure problem when querying simultaneously

If multiple queries are executed simultaneously by pressing the Refresh button on the dashboard, the following error occurs and fails:

Error running query: **(2006, “Lost connection to MySQL server at ‘handshake: reading initial communication packet’, system error: 11”)

Error running query: **SSH tunnel: Could not establish session to SSH gateway

My data source is on AWS RDS, and I’m using SSH tunneling through bastion server on AWS EC2.
Does anyone know about this issue? I’m using SaaS version.