Manually added events disappeared from iPhone Calendar

Hello all! My calendar app randomly deleted all the events I had saved to my iPhone calendar. The calendars I have saved are still present and showing events, but the items I had added manually over time are not visible. I’ve tried to troubleshoot a number of different ways (I.e. restored calendar back-up from iCloud, checked what calendars are visible, turned phone off and on again, checked storage) and nothing that I can find seems to be the source. Any ideas?