Plugins disappearing…

Hi ??

Over the last couple of days, some of the plugins I am using at my wp-site, is disappearing. Today Akismet and Jetpack went away. I was able to install Aksimet again, but when I try to install Jetpack, the plugin says that it failed to do so, because the destination-folder already exists. But I cant find it anywhere in my back end.

Do anyone have any idea why the plugins are disappearing in the first place and how I can fix this?

Thank you!