I’ve dealt with business band radio interfering with GPS many times, in severe cases when the mic is keyed to transmit it would 100% kill GPS immediately and in other cases when the mic was keyed the GPS signal would slowly degrade until it was gone, and in some cases a nearby grain cart  tractor maybe 100 -150 ft away would kill the GPS in the combine immediately. Fought this case for a whole harvest in 2011 with a customer, then in the spring of 2012 we had a frequency change on all StarFire receivers, this customer then had no problems at all after the change.

So I’m thinking it’s very possible that the pilot could have been on his radio as he passed over and killed the GPS signal in the sprayer.