Why do new calendar events disappear from the Samsung calendar?

[Android Central Question]

I have been using the stock calendar on my note5 for a couple years, which i have set up to sync with my Google calendars. It was working great until about a month ago, when I noticed that events added to the calendar dissapper shortly after they have been saved. If I add them in the Google calendar they will sync ok and remain. But if I add them in the Samsung calendar they disappear - I assume during the sync process. This problem needs to be fixed. Please help. (The stock calendar cannot be removed or updated. It appears to be part of the os. Could this be due to a software update issue?) Is there a fix for this? Please help.