Related Items Control can not filter 5000+ items list

Hello Community,
I am focusing an issue using Plumsail Form on SP 2016 (on-premise) using related items control.

I have a "parent" List Form with a related items control that has a second list (children) as source data (which has more than 5000+ items). That second list is filtered ad hoc in Display or Edit Form by ID field of the "parent" Form/List that should be eq to ID-Lookup filed in child List/View. So I have a 1:n constellation. Unfortunately no items will be displayed in the related items list. I believe the control can not start filtering because the list extends that 5000 items threshold and aborts filtering.

What can you suggest that related items control can filter a source list with more then 5000 items?
The parent-ID is the only lookup identifier for the "child" list that I have available.

Thansk for your assistance.

Dear @chris_boe,
Make sure that the field you're using for filtering is indexed - it is prerequisite for filtering lists with over 5000 items in SharePoint. Filtered results also shouldn't return over 5000 items.