Isolate the change: Did this happen immediately after a specific version upgrade (e.g., upgrading an IAM policy, a Kubernetes version, or a database engine)? Identify the victims: Is it all developers, or just those in a specific team/role? Check the error: I’d ask for the exact error string. There is a massive difference between a 403 Forbidden (WAF/Application level) and an IAM: Unauthorized (AWS level). I would follow the "Path of the Request" to see where the door is locked: CloudTrail / Audit Logs: This is the first stop. I'd search for AccessDenied events. Clue: If I see an "Implicit Deny," it means a new Service Control Policy (SCP) or Permission Boundary was added during the upgrade that we didn't account for. Policy Evaluation Logic: I’d check if the upgrade introduced ABAC (Attribute-Based Access Control). For example, did the upgrade now require a Project tag on all resources that the developers don't have yet? Identity Mapping: If using Kubernetes, did the OIDC provider or IAM Roles for Service Accounts (IRSA) break during the cluster upgrade?