Here's a good one for you, Richard.

My new little Canon camera has wifi built in so you can send your snaps
to your desktop or laptop computer, or to many off-site storage and
display sites. A number of newer cameras have this feature.

Well, I had no problems sending a few sample photos to my laptop, but
the connection between my camera and my desktop was sporadic and flaky.

I had wifi on both computers turned on. It suddenly occurred to me that
my desktop computer was also hardwired to my home network, so just for
grins, I unplugged the cable between the computer and my router.

WiFi problem went away.

Now, I have other devices that connect via wifi and they work properly
for communication whether my desktop is plugged in or not, so long as
wifi is on.

I'm still experimenting with this issue, but I think I have solved it.
But...why it exists, I cannot figure. I wonder if it is a DHCP issue.