Bridge Preferences > Cache
At the top, make sure "Automatically Export Caches to Folders When Possible" is checked.
(In this window you can also choose to purge the Cache, which will remove all your cached into from inside the Bridge database but doesn't remove any distributed cache files from individual folders.)
Quit Bridge and go into Windows Explorer, find the directory, make sure to be viewing all/hidden files etc. You will see two or possibly three files with Adobe Bridge in their names; it's safe delete them all. (Note that one you might see is Bridge Sort, and deleting this one will remove any custom sort order you set inside Bridge for that folder.)
Relaunch Bridge and navigate to that folder. Bridge should correctly rebuild all the thumbnails for the directory.