Why does a project sometimes not generate links?

Hi there! I just saw detail in some projects, I can’t find the reason why this problem happens.
An example:
I had created 3 projects (A, B, and C) same configuration, same everything! after 3 days on:
– Project A, has created 340 verified links and continues to create posts.
– Project B, 282 verified links, and then it is stopped, they do not generate sent links.
– Project C, 61 verified links and now it is stopped, it does not generate sent links.

What could be the problem?