A company with multiple AWS accounts, each containing one or more VPCs, has implemented a new security requirement to inspect all inter-VPC traffic. They have deployed a transit gateway to connect all VPCs and a shared services VPC with Amazon EC2 instances running IDS services for stateful inspection, distributed across three Availability Zones. VPC associations and routing have been configured on the transit gateway, and a few test VPCs have been migrated to this solution. However, after routing setup, intermittent connectivity issues are reported for traffic crossing Availability Zones. What steps should a network engineer take to resolve this issue?