Minifrontpagepro for K2 Thumbnail doesn't show

Hi, sometimes, when I create a news on K2, the thumbnail on Minifrontpagepro doesn't show-up.
It happens randomly, not for all news.
If I delete all files on /images/thumbnails/mod_minifrontpageprok2, then the thumbnail appears.

I have found that sometimes a file like nnn_default.jpg is generated on /images/thumbnails/mod_minifrontpageprok2 for a news. When this happens, the thumbnail for that news doesn't show-up. If I delete this Default Thumbnail file, then the correct thumbnail appears on home page.

However, in all Minifrontpagepro modules on home page, the "Show Default Thumbnail" option is set to HIDE.

Joomla, template, K2 and all modules and components are on the last version.

Sorry for my english

www.ioconsumatoresardegna.it

Now everything looks fine because I have deleted the 122_253_default.jpg image (first news on left on the carousel).

For test, I restored 122_253_default.jpg image, instead of the correct thumbnail 122_253.jpg that was there before, and the issue appears again. You can see it.

The problem happens randomly, I am unable to reproduce the steps. The actions to insert a new article on K2 are always the same. Writing text, loading a image, saving and publishing. Most of the time there are no problems.