Just happened today in our 2018 CX-5. Although it was only drizzling a bit, the wipers were functioning at maximum high speed which should be the case only when it is raining really very heavy. Any thoughts?

 

There's a "sensitivity" setting you can change.

 

I haven't seen rain since I purchased mine in January, So this is just from experience with other rain sensing wipers - these systems use speedometer as one input and will move the wipers to a higher speed if you are driving at a higher speed.
I'll admit to liking the auto wipers, but I'm a minimalist with wipers - so these automatic systems usually are overkill by my standards. Pretty often you'll find me manually operating the wiper blades when rain is more of a drizzle.