Jira includes components like reports and charts that retrieve information about issues. These components often use filters to present graphical insights into your workflow.
If a filter is configured to include issues containing MLCS fields with options that have been deleted from the field configuration, Jira will attempt to access the deleted option. This will result in a failure, causing a NullPointerException.
Here is an excerpt from the Jira logs:
How to avoid the exception
A workaround is to avoid the issues with deleted options in filters used by components like reports and charts.
The best way to avoid this problem is by disabling the options instead of deleting them (they cannot be selected anymore but the option still exists).