Which headers are considered invalid by AWS in ALB attribute routing.http.drop_invalid_header_fields.enabled?

Hope this helps - https://docs.aws.amazon.com/elasticloadbalancing/latest/application/application-load-balancers.html

routing.http.drop_invalid_header_fields.enabled Indicates whether HTTP headers with header fields that are not valid are removed by the load balancer (true), or routed to targets (false). The default is false. Elastic Load Balancing requires that message header names conform to the regular expression [-A-Za-z0-9]+, which describes all registered internet message headers. Each name consists of alphanumeric characters or hyphens.