This morning I tried to access a dashboard and could not connect to my C-8 at its IP address. I could connect via remote admin. I did a reset but that did not fix it. I did a shutdown, unplug, restart but that did not fix it. My UDMP shows the C-8 connected. I tried to connect to the diagnostic IP but no go.
I had that happen to me before I reserved an IP, but it was usually only after a reboot when it got back on the network. OP says it just happened one morning, so it seems unlikely the IP changed while it connected.
Still, going to the webpage for find my hub is an easy way to find it again if the IP did change.