TL;DR: Environment in initial scene was manually adjusted; changing the FPS refactored the scene and caused the ‘Time of Day’ to be respected instead. Change ‘Time of Day’ to what you would like for your lighting scenario and all will work.
1.) Open file above, everything looks as it should:
Note however the Time of Day under the Properties tab for Environment- it is at 9pm. Looking back at the original settings it listed as 9pm as well, which is incorrect for the amount of light being generated.
I suspect that the placement of this Environment was done either before we changed from Skies to Environments and/or someone manually keyframed the environment without regard to the Time of Day settings.