WiFi Network EPSON printer some...times not reachable in Win10.

Every data connection (wired or wireless) with the router has its own unique local IP address assigned by the router's DHCP server. The tp-link router (Archer AXE75) is new since a few months, latest firmware, etc .... Never had any issues with the router.
Now I realize that something is missing in the router: log files about network devices coming online or going offline, with info about precise timing (1 sec accuracy) and a recording of maybe other system info for the purpose of trouble shooting and analysis.
There is a system log but that does not hold any info about trouble shooting relevant to my case.

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Addendum
I just had a weired thing with the router... The printer fell asleep before noon after being put on this morning.
At noon I pushed the printer's home button and all was OK: printer woke up, printer icon appeared in the W7 Network pane, could check the printer's dashboard, could print and scan, did a ping to the printer (192.168.1.101 in my case) from the W7 PC, so all ok, ....
Except for the router's dashboard; de printer did not at all appear in the router's Connected Client list (Network Map > Clients).
So I logged out en back in into the router's dashboard several times but the printer did not show on the router's Connected Client list while everthing about the printer kept on working normal.
It was only after pinging the printer from within the router's dashboard (router ping: Advanced > System > Diagnostics) that the printer immediately re-appeared in the Connected Client list.
Maybe a glitch in the router's firmware ...

Reading Norton stuff, I can imagine that Norton sees any irregularity in the WiFi as a possible virus thread and performs then some action.
You may lower its detection sensitivity. You are aware of the following article?
Change the trust level of your network and devices
I have on my smartphone the app WiFiAnalyzer (open source).
It tells you WiFi usage in your neighborhood, In my neighborhood people use channels 1 or 11 and not 6, so I use that channel to minimize interference.

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Just read your addendum. I have access to the data disk of my wife's PC. When her PC comes in sleeping mode, I loose contact. I could never solve this, but since her PC is next to mine I can easily press the power button to have contact again. I have also a miniPC rwo floors above me. When in sleeping mode it wakes up immediately when I access this PC

It is possible to wake up a computer by keeping the WiFi adapter from going into sleep (WiFi Network Adapter > Properties > Configure > Power Management... ) There could be also a setting somewhere that allows for explicitly waking up a computer via the WiFi adapter; I remember seen something like that ... somewhere.

I don't think the WiFi ether is very busy in my neighborhood, but an analyzer could be handy.

I'm aware of Norton's directions about how to put a higher trust level on a particular network and/or network device. That has been applied to one of the W10 PCs, the other W10 PC is lacking this higher trust level for the printer; see post #1. But for the past several weeks it did not make any difference, at least not until this evening ... maybe...

One of the W10 PCs has been making trouble (again), and it is the PC with Norton Full Trust being ON for the WiFi home network and ON for the printer too. This troublesome W10 PC has Python programming software and Mind+ robotic software on board. Recently Norton was nagging en whining when Mind+ was at work with Norton pop-ups all the time. It might be that Norton has become edgy and nervous because of Mind+ thereby putting the Norton Security Level (NSL) higher. After I ran Norton Smart Scan, a hour ago, access to the printer came back and so all 3 PCs had again printer access.

Concluding: In my view NSL probably determines whether or not the printer is accessible; in turn Norton's edginess and NSL is then probably determined by the complete set of apps (and their risk) on the PC... That could also explain why printer access is good for a few days but over time, as the last manual Norton scan falls deeper into the past, NSL edges up till the point where the printer is kept out.

But now all is back OK.