Standard user cannot add a secondary network interface to a VM

My installation has multiple virtual networks (VNs). When creating a virtual machine (VM) a non-admin user can add two network interfaces on different VNs and they work fine.

However, this same standard user cannot add a VN to an already-existing VM. The oneadmin user can, no problem.

It’s clearly not a network configuration issue because the user can create interfaces to those networks. It looks like it’s more an issue with a standard user not being able to add another interface to an existing VM. Any idea if this is accurate, and why this might be so? Or am I missing something?

Versions of the related components and OS (frontend, hypervisors, VMs):
OS: CentOS 7.9
Open Nebula:
VMs: CentOS 8.

Steps to reproduce:
All done in the web interface:

  1. Login as a standard, non-admin user.

  2. Click on an existing VM.

  3. Click the “Network” tab.
    There are no buttons to add another NIC.

  4. Login as oneadmin

  5. Click on an existing VM.

  6. Click the “Network” tab.

There is a green “Attach nic” button to the right of the screen.