Well ,I can't see anything wrong with these raw data.

If 3,4,5,6,12 are all from the same graphical type of exo, it could be possible that the server was too busy to produce the drawing.
These things can happen; escpecially if the server is very busy with producing lots of images and heavy softwares like Maxima/Octave and is running some admin-task as well (like cron or wims_own mkindex)

If it is your own server, you can raise these cpu-time limits ;and re-scedule all heavy cpu-load tasks to the "non_busy hours".
If it is a free wims-mirror; consider it bad luck...

kind regards,
Joke