Bridge is not using the cache that it just spent many hours building

I have a collection of about 8,500 PSD and PSB files, organized in separate directories per date. I recently moved the photos  to a new drive, so I ran "Build and export cache" in Bridge, which took many hours to complete.

Unfortunately Bridge seems to be ignoring the cache that it spent so long building. When I click on a new directory for the first time, it generates the thumbnails from scratch. Restarting Bridge doesn't help.

I've verified that there is a .BridgeSharedCache directory in each directory, with subdirectories called "256", "1024", "data", and "full". In most cases the 256 and 1024 directories contain small .png files, but in some cases they are empty, even though the parent directory contains photos. Bridge seems to ignore the cache regardless of whether or not the .png files exist.

I'm running Bridge 11.0.0.83