iCloud calendar in Outlook, duplicate appointments can't be deleted

I use iCloud in Outlook so that appointments made on my PC will sync with my iPhone. When I make an appointment in my iCloud calendar on my PC (via Outlook), it automatically duplicates on my PC iCloud calendar account, but not on my iPhone and not on my PC Outlook calendar account. I am using IOS calendar on my iPhone, not Outlook app.

If I need to delete or move the appointment, one entry behaves appropriately but the other entry will not delete or update. When I try to delete the second entry, it appears to accept the command but still remains in view. If I try to change the appointment information, I get the error "The item cannot be saved to this folder. The folder was deleted or moved, or you do not have permission. Do you want to save a copy of it in the default folder for the item?" If I reply yes, nothing changes. I don't know what "default folder" is being referenced.

I've researched issues with Outlook and none of the suggested actions make a difference. Could this be an iCloud issue?