Welcome to the joys of owning a T1.
Make sure you've upgraded the reader to the latest version of the firmware. I also found turning the reader off after loading new books on to it helped a little. Also clearing the cache occasionally.
Also, have a look at this thread,
https://www.mobileread.com/forums/sho...d.php?t=180060. I think there's at least one other thread on this topic or similar, but I couldn't find it.
Hope this helps.