debug.log extract:

USER NOTICE: Bad album object parameter to newImage(example.jpg) in /var/www/example.com/zenphoto/zp-core/class-image.php on line 44
trigger_error called from newImage (class-image.php [44])
from filterImageQuery (template-functions.php [3221])
from getRandomImages (template-functions.php [3266])
from include (inc-header.php [24])
from include (index.php [1])
from include (index.php [130])
from index.php [28]

I have 2 pics where upper was created.
Is this related with the pics or with ZPC?

The notice says that somehow an image object is tried to be created with a non correct album object. Why that happens, I cannot tell you as this might be related to the theme used.

Ok, thanks.
I'll check and see what I can find or if will happen again.