Why are my calendar events periodically deleting?

The second time this has happened. I have several accounts linked to my Samsung calendar including Gmail and live.com accounts. I opened my calendar yesterday and most of the events have vanished. Same on my Google Calendar app. But when I open Google calendar on my computer they are all still there. Anyone know why this could be? My phone had been on maximum power-saving mode, could this have affected it?

This would be better in a specific device forum, but you haven’t mentioned the device so I can’t move it.