Yesterday I received 2 Subeautique Invitations in random events and today I have received 5. It's awesome to keep getting them...but now I'm thinking this might be a bug.

Like Destiny said, it might just be your luck! I only get one maybe once every two weeks, sometimes longer.

It is simply random. I get one once a month if lucky, even during events with its higher page refresh rate.

That's incredibly lucky! I think I got 2-3 in the last few days but I restock so I page jump every few seconds for hours so I always assumed I have a higher success rate when it comes to random events than most players!