Good tip sk1939, thank you. I tried connecting three hard wire Ethernet lines to the router using ports 4, 3 and 2. Everything works when set up that way. Before today I had the two hard wired devices plugged in to #1 and #2 ports. When #3 was added, the trouble started. For some reason it seems to work fine coming from the other side. May end up buying a router anyway if any instability starts to show up.
You could also buy a 5 port switch, plug that into port 1, and plug the rest of your devices into the remaining ports on the switch. Would probably be cheaper than buying a new router.