Since the host is marked as not responding, let's first focus on that.
Check the vmkernel.log file for the affected host and search for "hostd detected to be non-responsive" entry. If present, the hostd process is hung and a host restart is something worth trying.
A strong indicator that the hostd is hung after being marked as Not Responding, is if you run the esxcli command and it hangs however localcli works at the same time.
If hosts are showing not responding from vCenter server then Please check if you are able to make connection from vCenter to ESXi and vice versa on port 902.
Try also restarting management agents and then management network. It will not have impact on running machines, so you can try that in office hours.
Thank you both, I will try these suggestions and report back.
Unfortunately I cannot retrieve the vmkernel.log files from any of the hosts in the affected cluster. Also tried restarting management agents and management network. I will look to schedule in a reboot of the hosts.