I concur that low head drainage can attribute to part of that.
I also see that you have bermuda grass which thrives well in lower Ph soil.
Lower Ph soil is an indicator of higher clay content.
This will eventually lead to one of various types of nonbluming subterranean fungus.
I would recommend changing your Rachio to the Clay setting instead of Clay/Loam.
Then I recommend aerating your lawn and then applying a pelletized gypsum.
Gypsum helps to break down hard and clay soils. Once broken down, they will readily accept
the irrigation that you are applying while helping nutrients get down to the roots.
In the even of having low head drainage I would recommend the aforementioned treatment as well as irrigation heads with check valves built into them.
Rainbird has the SAMS heads which are good for this purpose. Toro has the Precision checkvalve insert. Hunter has the Pro Spray head.