Comprehension cards are being created but production cards are not!

After months of studying the language, I realized that for some reason comprehension cards are being created but the production cards are not - but it seems random. Some of the cards have production cards, some don't. 

1. Do you have any idea why this is happening?

2. Is there any way to fix it? Even if I can isolate the cards which don't have production cards, I don't know how to create production cards.

thanks