AWS aurora (Mysql, serverless) drops connection after 5 minutes

My application creates multiple (6-7) connections to the server. After about 5 minutes, 1 of the connections will be dropped. I can't really figure out why. Other than the aurora_fwd_master_idle_timeout that is set to 60, other configs remain at their default values. wait_timeout value, for example, defaults at 8 hours, so it should be long enough. If I limit the multiple connections to 3-4, sometimes it work, sometimes it doesn't. When it doesn't work, the detailed error is as follows:

MySql.Data.MySqlClient.MySqlException (0x80004005): Fatal error encountered during data read. 
---> MySql.Data.MySqlClient.MySqlException (0x80004005): Reading from the stream has failed. 
---> System.IO.IOException: The read operation failed, see inner exception. 
---> System.TimeoutException: Unable to read data from the transport connection: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond. 
---> System.IO.IOException: Unable to read data from the transport connection: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond. 
---> System.Net.Sockets.SocketException: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond

Any ideas of what could possibly cause this?