The UniFi Controller is in a standalone VM (well, it is in a container actually)
HA is in a VM installed following the guide by kanga_who:
I had zero network issues until I migrated to Proxmox from Ubuntu/HA and now I think there is something somewhere that UniFi doesn’t like.
The issue is manifested in all my ESPHome devices becoming unavailable for a few seconds at virtually the same time and following a suggestion by tom_l I did catch my HA device becoming unreachable by a ping at about the same time (I’m waiting for mere events so that I can confirm that.)
Thanks and I don’t doubt anything you say but I am much more comfortable with Proxmox than I am with Docker. I had never even heard of Docker until I was introduced to it by HA but I have used VMs before. Conceptually a VM is very simple to my mind whereas Docker is a virtually (no pun intended) whole new architecture to learn.
Historically I moved from a Pi to Proxmox and only went to Ubuntu/HA because I wanted Bluetooth. I must say I am relieved to have made the move back to Proxmox where I am far more comfortable. I know very little about Linux so having VMs compartmentalised at a high level allows me to have some confidence I can’t break everything with my ‘just-enough’ Linux knowledge!