I edited my entire project in stereo, added plugins, and everything sounded great. Right before I went to export the file, the entire file is now mono, even the master mix. I used to clearly see a Left and Right dB bar, now just one. Please help.
The Sequence in the image seems to have a Mono master track rather than Stereo, hence the mono output.
Go to File > New > Sequence and click on Tracks tab in the dialog that pops up. Make sure the the Mix is set to Stereo and click OK, but only if the Frame Size and Frame Rate under the Settings tab matches the green nested sequence i see in the screen dump you provided.
When done you end up with an empty Sequence so now you have to manually place the Sequence you have in your screen dump in the new stereo Sequence. Now the export will come out as stereo but you have to make sure that the Sequence you place there have a Stereo master track as well. When you nested that one Premiere Pro thought it was Mono and it is a big chance that it indeed has a Mono master as well so it´s i must to check out the whole chain of Sequences, from the first to the last.