MacBook – Screen brightness keeps going to max

My system

I'm running a 13" retina MacBook Pro and using El Capitan 10.11.6.

Model Name: MacBook Pro
Model Identifier: MacBookPro11,1
Processor Name: Intel Core i7
Processor Speed: 2.8 GHz
Number of Processors: 1
Total Number of Cores: 2
L2 Cache (per Core): 256 KB
L3 Cache: 4 MB
Memory: 16 GB
Boot ROM Version: MBP111.0142.B00
SMC Version (system): 2.16f68

Issue

Often while working in a low ambient light environment, I'll turn down the screen brightness to make the display more comfortable to work with. Several times, immediately after turning down the brightness, the system will raise it up to max again.

I turn it down.

The system turns it up.

This goes on for several minutes and continually interrupts/blinds me.

My Display settings allow automatic brightness adjustment. But this is in a room often with no lighting other than the laptop so it should be adjusting down if anything.

Even after turning this setting off and closing System Preferences, the brightness still is changing automatically. I have also tried resetting the System Management Controller (SMC).

How do I a) prevent this from happening and b) actually turn off automatic brightness adjustment?