One of the typical ways to use filter items is to assign them to positions based on department, division, branch, etc. In these cases, there are managers who are responsible for positions falling under a given filter item, so a rule can be created that says, for example: If a position has the filter item "Headquarters", manager XY should have access to it (and its candidates).
It is precisely for these scenarios that there is functionality that allows you to set up such automatic sharing.
This sharing can only be set up by administrators, by selecting one or more filter items that the given colleague monitors in the settings of specific users (link).
In practice, such monitoring means:
If you want to unshare a position shared in this way, you must do it, just like with manually shared positions, using the manual sharing dialog.