Hello everyone .. problem with kindle

Hi, I am a new french user so please excuse my english.
I have a Kindle and I use Calibre . I have a small problem, I have few books (wierd but they are all from Harlan Coben) who disappear on the kindle. I can see them on Calibre and they are flagged as they are on my Kindle directory.
I have to reload then, they appear on the kindle, I open it, no problem to read BUT if I return to my library the books disappear !!!

Thanks for your help