The rain delay that you had through Friday appeared to work (I just learned something new as I didn't know rain delay worked with flex schedules -- part of running a flex schedule is for it to determine how much rain you got and you not to have to worry about setting something manually). This zone watered on Saturday, May 7 because the Current Moisture Balance (think of it like a gas tank for your soil) was totally empty. So it put some gas in the tank. Since the day isn't yet over, it still says Forecasted, and based on weather parameters, and what you've told it about your soil and plants, it's going to predict to empty .19 inches out of the gas tank. About an hour before your schedules are set up on Sunday, it's going to go out and look at the weather forecast again, and also calculate what actually happened on Saturday (perhaps you got rain that wasn't in the forecast, or a different amount of rain than was predicted.). Since it's taking all these changes into consideration on a daily basis, the "schedule" of when it's going to water next is just an estimate, and is subject to change (just like the weather!).
The rain that you got on May 5 was only .12inches -- that's not a lot, but since you turned on the rain delay, you thought you had a lot more? From the name of the weather station, its not a PWS (Personal Weather Station). Is it a long ways away from your location? You might want to go in and see if you can find a PWS closer to you that might be more accurate.
The reason it's got to keep watering more often is that even though you filled up the gas tank, you also drove and used up almost half a tank of gas (this zone watered .45 in, but between the weather and the plants using the water, it used up .19in.). So the 58% full makes sense. On Sunday, you're going to drive the car around some more, but not put any more gas into it, so you will be down to only 11% in the tank. If there is no rain in the forecast for May 9, based on the ET this zone is using every day (from .12 in to .21 in), this zone is going to need to water again on May 9.
I hope I haven't confused you more, talking about the gas tank and the water all at the same time. But it is a great analogy to help understand it.