Sometimes, during period of high traffic on sites, CCK input fields disappear while adding a content from the backend. I haven’t enabled the throttle module. The fields are restored automatically at other times.
For example – field for image upload, checkbox for featured for a content type News disappear during heavy traffic but get automatically restored during other times.
What could be a cause?
Does Drupal have an internal throttling mechanism during times of heavy traffic?
No. Throttle was an attempt to do this, but it is genrally not used. As you have this off it is not going to be the cause.
I would suggest tweeking your performance settings to see if you can get peak load to not affect your systems so much.