The phrase "certain regularity" means that something happens in a consistent or predictable pattern.
Sentences with «certain regularity»
At present our level of understanding is about that of Mendeleyev, who discovered only that certain regularities in the properties of the elements existed. (scientificamerican.com)
He is shown as intervening with a certain regularity, even in minor matters, usually relating to procedure or presentation. (faith.org.uk)
But mutations have a certain regularity or odds, making this much diversity unlikely. (sciencedaily.com)