Is your custom table in any specific scope? Can you try changing the scope of instance to the scope that table is in & then check.
If not, you can use a background script so as to get it checked to True.
Something as below. Try it in DEV first.
var uprec=new GlideRecord('sys_dictionary');
uprec.initialize();
uprec.name='incident'; //replace your table name change_request, etc.
uprec.internal_type='boolean'; //truefalse or string
uprec.column_label='ABC';
uprec.element='xyz';
uprec.function_field=true;
uprec.insert();
