Thanks Frank for taking an interest.
I had a look at static vs DHCP and my router settings and found a more likely culprit. I noticed that when I checked the list of connected wifi devices and their IP addresses within the router that they all had an 'Lease Time' of 2 hrs. I could see that this time was counting down for each device depending on when it connected. Anyway, my router lets me set 'Address reservation' which makes this connection 'permanent'. So I did this with the entry for Rune. I'm hoping that this will be the fix. But time will tell!
I'll be sure to report back either way.