Rachio 2 - Activating 2 zones, should be only one

I have a Rachio 2 that runs 8 programmed zones in sequence. It has worked flawlessly for the 2 past years. At the start of year 3, I turned on the system and tested each zone. All worked well except for one thing. I was surprised to find that zone 5 ran both on its own and then again simultaneously along with zones 6 and 7 when they were ran. What might cause this to occur?

Possible that there is a problem with the zone 5 valve, specifically the diaphragm. When the other zones kick on, it can cause a negative pressure on the zone 5 valve, and if it is failing, can cause it to kick on.

Other possibility is a wiring short, but Iā€™m leaning more towards the valve.