I would "compact the cache" as a first step.
If you still have problems, purge the cache files. It's time consuming because Bridge must re-build each cache file for every folder containing images, but Bridge will then have a clean database to work from.
If that doesn't work, then you must reset the program preferences. On Mac, hold down the Command (apple), Option and Shift keys as you startup Bridge. You will get a dialog box asking if you want to reset preferences.
I would also run the usual Mac maintenance programs to repair permissions and run the chron program. I use Onyx
to do this on a regular basis.