Connection refused on Hestia Control Panel

I have 6 servers, all running Hestia CP 1.7.8 on Ubuntu 18.04.6 LTS and on just one of them I’m getting a connection refused error when I try and access the control panel. I can access the sites running on that server and can SSH into it. I’ve checked v-list-firewall-ban and my IP isn’t in it.

I tried v-restart-web-backend to no effect, and apt update && apt upgrade which didn’t throw up any errors, but same issue. I can get onto websites on that server, but not the control panel.

Any pointers as to what I should be looking at next?