Footage suddenly gray and washed out...

Working on a project and one of the video clips was a bit washed out as if the brightness was turned up. I searched the boards here and learned about the Working Color Space feature under Sequence Settings and set it to Rec. 709, which fixed the clip nicely.

[Not sure this part is relevant, but sharing just in case.] I was about to export and realized my frame size of 4032 x 2268 was a bit big, so I changed it to 1920 x 1080, resized all the clips and thought I was ready to export...

Except now all the clips except the one above look darkened as if the brightness/contrast were turned down. The most obvious example is the title screen.

Before (an early export of project)

 After

I'm lost here. What happened?