How do I host multiple services using subdirectories with nginx-ingress?

This is not likely to be an issue with AKS, as the components you use are working on top of Kubernetes layer. However, if you want to be sure you can deploy this on top of minikube locally and see if the problem persists.

There are also few other things to consider:

1. There is a detailed guide about creating ingress controller on AKS. The guide is up to date and confirmed to be working fine.

This article shows you how to deploy the NGINX ingress controller in an Azure Kubernetes Service (AKS) cluster. The cert-manager project is used to automatically generate and configure Let's Encrypt certificates. Finally, two applications are run in the AKS cluster, each of which is accessible over a single IP address.

2. You may also want to use alternative like Traefik:

Traefik is a modern HTTP reverse proxy and load balancer made to deploy microservices with ease.

3. Remember that:

Operators will typically wish to install this component into the kube-system namespace where that namespace's default service account will ensure adequate privileges to watch Ingress resources cluster-wide.

Please let me know if that helped.