Icebreaker bot Repeat Pairings

Hi,

I have installed icebreaker bot to send matches once a month and everything seems to be working well. However, after only two months, people have started to get paired with people they had already been matched with. We checked the numbers of people that have opted out and the number is so low it doesn't justify the repeat pairings. Is there a rule in the background to stop this from happening?