I've restarted it several times, and actually other projects are working like clockwork in Premiere, so I think it has to do with the source file links.
I moved all the source files to a new folder, and when I opened this project again, almost all of the sequences were back to normal ... except for one. It duplicated itself, merged all the clips together & turned green (like the image I posted earlier). So what does this green bar mean? Why is it duplicating sequences & merging the clips together within the sequences?