Yahoo shared calendar not syncing anymore with iPhone's calendar

iPhone 12 and iPad no longer get new shared calendar events.

i found by going to settings on the iPhone and scrolling down to Apps, then going to calendar, near the top is accounts. Select the yahoo account and you will see a toggle for calendar. Toggle it off and it will ask about deleting all events. Confirm yes and then Toggle Calendar back on. It will re-sync over the next few minutes showing all the old and new events.

Then I repeated the process on my other Apple device.

i am not sure if it is an Apple IOS, Yahoo, communication/handshake issue, what causes it to happen, and/or how would you know without checking with your partner or missing an event.