Shared calendar not showing some events

I use Apple calendar to organize family schedule. Each family member has a calendar and we share with each other. Recently, some of the events being shared with one member of my family has not been showing up. For example a regularly scheduled piano lesson stop showing up on my calendar, but was still on the family member’s calendar. And they could see it on their phone. Other events for the day showed on both our phones. It was just the piano lesson that didn’t show. When I went to the family member’s phone and just clicked on the event to look at the details, doing NO changes to the event. It suddenly reappear in my calendar again. This has been extremely frustrating and we have missed (and been charged) for drs appointments. So this is more than a nuisances, this glitch is a financial cost to us.