Apple Calendar: Invitees missing from events created from web/app “add to calendar” links.

INVITEES line missing from certain Apple Calendar events.

• yes I’ve tried in EDIT mode
• yes I’ve restarted and updated… this has been happening for at least a year since I started sharing events regularly
• it works when I create the event
• it does not work when the event is created by using the “add to calendar” option from websites and apps. An event is created, but this is when I’m unable to add invitees.

The closest hint of an explanation (but not solution) I’ve found is that the problem has something to do with the event being created by iCloud/exchange. But I don’t understand what that is so it’s just a hunch.

I’m at a dead end searching for an explanation or solution. Appreciate any insight! Thanks.