Board Query excludes Epic Issue Type
The filter from your Agile Board is used to find the epics to display. Sometimes this filter has been configured to exclude the Epic issue type and therefore the product can't access them.
For example, you may have a JQL filter query which inadvertently excludes the Epic Issue Type like the following.
project = EXAMPLE and issueType in (Story, Task, Bug) ORDER BY Rank desc
To fix this issue, adjust the board query to include Epic Issue Type, using the example above:
project = EXAMPLE and issueType in (Epic, Story, Task, Bug) ORDER BY Rank desc
Or simply remove the check on issueType entirely.
project = EXAMPLE ORDER BY Rank desc