One Client Stopped Connecting / Backing Up

I’m unsure were to look, I’ve made no changes to the server or the clients, and yet, one has just stopped 3 days ago and won’t find the local server? all the settings are the same across all 5 clients, yet one has decided to give up? any thoughts on were to look? I’m not using the internet, I’m using a local machine on the local network.

Thanks in advance.