not accepted for Intellectual Property Refusal, but a week before about 10 images from the same venue en with the same description were accepted.

This is not the first time this happened. A lot of my images are not accepted for Intellectual Property Refusal, but a few days before about 10 images from the same venue and with the same description were accepted.
Can someone explain?
These were accepted a few days ago: File # 1877433579 File # 1877433111 File # 1877433362 File # 1877432910 File # 1877432339 and about ten more. Then about 30 images from the same series at the same venue and the same description are not accepted. 
Who know the answer??

Greetings from the Netherlands :-)
Mies