What is the problem?
Whilst my ender 3 connected to octopi via USB no serial port connection. Octopi connected to server via ethernet cable
What did you already try to solve it?
reinstalled Octoprint ver 1.3.10 and octopi ver 0.16.0
when reverted to connection to server via wifi it connected no problems
Additional information about your setup (OctoPrint version, OctoPi version, printer, firmware, octoprint.log, serial.log or output on terminal tab, ...)
Could you clearly restate what is and isn't working? I'm having a difficult time following you.
"...when reverted to connection to server via wifi it connected no problems"
This to me sounds like:
"Everything works fine if I don't connect my Ethernet cable on my Raspberry Pi 3B computer. Once I connect the Ethernet cable then I can no longer connect to my http://octopi.local instance."
If that's accurate then add a keyboard/monitor/mouse to the Raspberry Pi and run ifconfig before/after connecting the Ethernet cable. And also run route before/after. My guess is that your router is not providing the correct information as a DHCP host.