SQL Server AG Listener issues in an AWS VPC
Can you please review the AWS documentation on how to properly set up AG on their environment? 
http://docs.aws.amazon.com/quickstart/latest/sql/part3.html 

There are some specific steps that need to be done for this to work. 
You may also want to read about the MultisubnetFailover (https://docs.microsoft.com/en-us/dotnet/framework/data/adonet/sql/sqlclient-support-for-high-availability-disaster-recovery) as without using this feature it may take several minutes (depending on how much you set up your HostRecordTTL setting) for the DNS setting to be updated and the listener name start pointing to the new active node IP. On my tests, without changing the HostRecordTTL and the multisubnetfailover it was taking up to 15 minutes for the listener name to start working again after a failover so I had to play with these parameters to have something that would work for all my client applications