Not sure what’s causing that problem without a bit more information, but I’m guessing you may have your calendar set up twice – once through a Skill, and once directly through the Alexa app – or once through your calendar and once through your spouse’s calendar.
Without a bit more detail, it’s hard to troubleshoot directly, but one step may be to remove all the calendars you have set up through the Alexa app, and re-add them over the course of a few days to figure out where the trouble is coming from.
Hope that helps you start pinpointing the problem!
-Daniel