I had a similar experience today and after the last update. I just went to settings, turned off adaptive brightness, readjusted my brightness level and then turned adaptive brightness back on. Solved the problem. Overall, my opinion is that this is an excellent phone.
Weird, I'm still not seeing it... Pixel XL, originally Verizon but now T-Mobile. I've still got the Verizon sim, popping that in doesn't make a difference.
I'm actually not sure when the update was installed on my Pixel XL. I just know that when I checked a couple of days ago my phone showed the July update. When I checked yesterday, it showed the August update was installed. This is the first time I have ever had a system update of any kind install itself without my knowledge. Mind you, I'm not complaining, I was just surprised to find the August update installed.