When you create calendar events and you select which calendar that event should go to are you selecting Samsung account, your Google account or my phone? Samsung cloud only backs up calendar events from "my phone" aka data that is local to your device. Sends it sounds like you use Google and/or outlook anyway I'd use either of them for your calendar and create events attached to your Google or Microsoft account that way you know your events will be visible on any device that you are signed in to and won't have to worry about backup as the calendar resides in the cloud.
The calendars all have different formats, which creates uncertainty for me. I sync them but have to take time to double-check every last detail. I stay with my favorite format, which Samsung should back up but surprisingly didn't. There is a note about Verizon subscribers should not expect Samsung Cloud backup of the calendar. I've lost my way two other times and can't stand the thought of losing the calendar again when upgrading.
