Calendar glitch with memorable dates

Does anyone else notice that setting birthdays or other memorable dates for your contacts in the address book results in a cumulative error developing when these are displayed in the calendar?

eg if today I set up a birthday for a contact as 1st Aug 2021 it will display in the calendar correctly this year, but the next year the occasion has moved by 24 hours and will be recorded on the calendar and against the contact details as being on 2nd Aug, without manual correction this same error occurs on each subsequent anniversary.

I’ve not been able to identify what is causing this, or stop it from happening, but it doesn’t seem to affect periodically occurring events set up in the calendar only. The issue seems to be app-specific rather than a device or iOS issue as it occurs on every Apple device I use

Does anyone have an insight into what is causing this, or more importantly, a solution?