Bridge loses Previews and CONSTANTLY has to REBUILD

[Ocean 11]

I am working through a few older shoots that are on an external hard drive.

EVERY TIME Bridge needs to rebuild those previews and I have to wait until it rebuilds the previews.

Why does Bridge lose the previews every time? 

It doesn't to that on a faster SSD drive, only on the older spinning hard drives.

[Lumigraphics]

Preferences->Cache, try setting the Cache size to maximum.

[Ocean 11]

It's not a problem of the cache size. I just opened a folder that I have been working on yesterday night - ALL PREVIEWS GONE. Now I have to wait another 15 minutes until this software rebuilds every single of hte 100 images in the folder. I'm sure when I shut down the computer and turn on in 3 hours to continue work, Bridge has again forgotten all previews and has to build it again.

why is this not working?