This sounds odd(to me) and step #1 for "odd" is trashing prefs. Okay, maybe that's step #2 after saving and closing the session, then re-open and try the export again, with a few things in mind:
1-are you certain that Elastic Audio is NOT enabled?
2-has your 4 bar selection been separated(IOW, you are not trying to export part of a larger audio clip)?
3-are the tracks part of a group that includes other tracks(or part of a CLIP GROUP)?
4-have you tried switching the tracks back to samples?
The above is based on my own experience of doing what you describe and having it actually work for me
