I am creating a node programatically which has an imagefield with 16 images attached. Each image is a blank PNG of about 1000px by 768px weighing in at about 5KB. The node displays fine.
On a separate path I have a View that displays the images attached to the node using a image style to shrink each images down to about 250px by 150px.
Sometimes when I first use the View to display the node maybe 5 (say) of the styles are not successfully generated. For each unsuccessful attempt I see a watchdog entry "Failed to create the style directory" followed by "Unable to generate the derived image located at ....". However the other 11 image styles are successfully generated in the correct directory.
Typically if I then hit the browser refresh button the broken image styles are then successfully generated.
This is Drupal 7.30 on shared hosting.
What is wrong ? Thanks.