Water pressure inside house drops to zero when sprinklers are on
I don't think you have a leak, what I believe is your pressure regulator is set at a high enough pressure that when the zone turns on and has a high surge until the pressure builds this is causing the no flow in the house for a few seconds. Once the flow stabilizes the pressure builds back up and you have pressure in the house again. To keep this from happening install a regulator on your sprinkler system and set it to a slightly lower pressure than what you want in the house. This will make set sprinkler lines take slightly longer to fill and if 2 psi lower will slightly reduce the water spray distance but your pressure would not drop as it is doing now.