There may be a time where you have added a post or task to your Calendar and aren't able to locate it within the HubSpot Calendar app.
This typically happens because your filters are set up to only show specific tasks or posts. So, your posts or tasks aren't actually missing, but are simply hidden behind unselected filter options.
To make sure you're showing all (relevant) content, check the boxes next to the appropriate content or task type on the left-hand side menu.
Also, click Edit next to Campaign and makes sure you Select all (or individual) appropriate Campaigns so any task or post associated with a specific Campaign will show up on your calendar.