I was having tons of lockups, then I moved the OS to a different router and all the ethernet problems seem to have gone away. In my case I have:
ATT Router -> TPLink ER605 -> TPLink Switch
When I moved the OS from the switch up to the ER605, all the ethernet problems seem to resolve. My intention was to put the OS on a vlan as the ER605 support them. I never setup a different vlan for the sprinkler though and just moving to a different router seem to resolve the issues. At least for a few days now.