Explanation
The method that would allow multiple VMs to share the same host IP address is NAT. NAT (Network Address Translation) is a technique that allows multiple devices to use a single public IP address by mapping their private IP addresses to different port numbers. NAT can be used for VM networking to enable multiple VMs on the same host to access the internet or other networks using the host's IP address. NAT can also provide security benefits by hiding the VMs' private IP addresses from external networks.

An intermediate distribution frame (IDF) is a free-standing or wall-mounted rack for managing and interconnecting a telecommunications cable between end-user devices and the main distribution frame (MDF).
DNS has nothing to do with LAN network connectivity. OS version and Switch vendor is not a thing. And the HIDS is detection not prevention. The only choice left is VLAN.
https://www.techtarget.com/whatis/definition/intermediate-distribution-frame-IDF#

Explanation
This is the most likely cause of the issue because firewall rules can block or allow traffic based on source, destination, port, protocol, or other criteria. If the firewall rules are not configured properly, they can prevent remote users from accessing the cloud application server, while allowing on-site users to access it. References:
https://docs.microsoft.com/en-us/azure/virtual-network/security-overview