Hi All,
SOUNDS like a common problem, but not so in my case, but here it goes.

1. Configuration: Epson WF-3640 PLUGGED into router (previously wifi connected).

2. Acer laptop, (upgraded to WIN-10) long time working with this printer now can't talk to the printer via wifi (only via USB cable). Because other devices can still use the printer via the network, I know it must be a laptop problem.

3. Additional info: Acer-Lap doesn't get a response by pinging the printer, other devices do. I changed the printer IP and the Acer still can't ping the new ip. I turned off Windows firewall with no change.

Someone thought I should try to ARP the printer, but I haven't figured that out yet. Suggestions appreciated.

Thanks
No, it won't WORK and you won't know why.
https://en.wikipedia.org/wiki/Address_Resolution_Protocol
Your laptop Wi-Fi device is failing.
To verify this, disable the on-board device and try a USB device. You can get a cheap USB WI-Fi adapter ALMOST anywhere. Try Walmart.
Cheap and Good WI-Fi stick from Walmart
Photo:

You should have one of these in your tool kit.

EDIT: There is a another reason for the failure. A security update may have made the printer unreachable by the updated on-board device. I will let somebody else try to help you resolve this. Otherwise, use a cheap adapter that doesn't care.Problem resolved.

Restatement of problem. Only 1 device of several unable to PRINT to, or ping a long existing network printer.

Geek-9pm's suggestion to use a different wifi connection was a good troubleshooting suggestion. (Goal is to break to chain somewhere to "half-step" the problem.) I didn't think the internal wifi was bad because internet browsing was 100%. Only unable to print.

1. I tried a cable network connection. (didn't work, turned into a long ordeal of unrelated problem).
2. Tried to uninstall printer software. (not in program list). Planned to re-install printer software.
3. Remembered printer has had a static IP address for many years. I changed it back to DHCP.
4. Deleted and reinstalled printer. JOY - after several weeks, I am printing again.

Thanks for reading.

r/Todd
Glad you got it. As you said:
..break to chain somewhere...
...is a proven method.