you said you have some power line plugs
No, I bought a set several years ago when investigating poor wi-fi but they didn't work for me and I returned them. I don't have any now and my network is entirely ethernet cabling (with wi-fi switched off
As an aside, I've now developed an additional way of checking that all is in order - a quick look at my BQM just to make sure that it is all red. During one of the 'intrusions' a few days ago I saw a short period of about half an hour when pings were being responded to at my IP. That stopped again as soon as I disabled wifi.