A very annoying bug: 180 duplicate of the same anniversary

Today I noticed this very incredible bug: an anniversary repeated 180 times. I mean the same anniversary repeated the same day 180 times. A nightmare.
How can get rid of it?

EDIT
With Thunderbird I managed to get rid of it, selecting many occurrences at a time. But I think that developers should worry about a similar bug.

Regain your privacy! Adopt /e/ the unGoogled mobile OS and online servicesphone

After deleting that anniversary it was re-created over and over again: a nightmare.