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Only issues that match selected criteria are displayed. Every issue for each active filter Criteria are defined by selecting proper options from filters. For issue to be displayed it has to match one of selected options in that filter options. Issue that match selected criteria can be still hidden if it option from each active filter.
There might be situation when issue that match every criteria is hidden. It is because the issue has no connection to root -issue. It means that any issue linking the issue with root is hiddendue to another issue that doesn't match criteria.