IP Addresses PiCore

Hi - This is quite trivial I know, but I thought I'd ask and see if there is a simple solution. I'm running LMS 8.3.0 on PiCore 8.1.0. This is on 24x7. Attachment to my router is wireless and wired is not convenient.

For some reason The IP address of piCore is getting changed by my router. This means that favourites on my PC for the pcP main page and access to the server, change. I also have to fine tune some of the settings in Material which are reset to the defaults. It's happened only 2 or 3 times but all in the last few months and is a minor irritation. Prior to that the IP address never changed. This felt like a router issue so my first step was to make some changes there via a setting "Always use this IP address:" .When I tried that it caused more problems with other address conflicts. The advice I was given was that I should set a static address outside the DHCP range on PiCore not in the router. I found the static address setting in PiCore but it gives a strong warning to only use it on a wired connection. I followed this advice and took no action

I'm tempted to factory reset the router which is a bit brutal. So I thought I'd run it all past all of you helpful people first.

Any advice?