This may be an issue due to port conflicts (meaning HA and Unifi Controller want to access the same port). Yes, Is that the right answer? I’m at the edge of my understanding here. 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! I must say I am relieved to have made the move back to Proxmox where I am far more comfortable. Historically I moved from a Pi to Proxmox and only went to Ubuntu/HA because I wanted Bluetooth. Conceptually a VM is very simple to my mind whereas Docker is a virtually (no pun intended) whole new architecture to learn. I had never even heard of Docker until I was introduced to it by HA but I have used VMs before. 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 and I don’t doubt anything you say but I am much more comfortable with Proxmox than I am with Docker. 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.

HA is in a VM installed following the guide by kanga_who: UniFi Controller is in a standalone VM (well, it is in a container actually)

Proxmox web interface port