My UIList does not scroll down in version 3.3.6

Question

I wrote an addon with several UI Lists. In Blender 3.2, I had no trouble scrolling down the list if it became longer than the box on the screen. However, I recently switched to Blender 3.3.6 and I realized that I can't scroll down if my UI List is long enough. The scroll bar appears on the right side, but if I try to move it, the list does not scroll. Here is an excerpt from my code:

bl_info = {
    "name": "UI LIST Test_Addon",
    "blender": (3, 3, 6),
    "description": "UI List does not scroll",
    "warning": "",
}

import bpy
from bpy.props import StringProperty, BoolProperty, FloatProperty, IntProperty, CollectionProperty
from bpy.types import UIList, Operator, Panel

class CustomListItem(bpy.types.PropertyGroup):
    objectName: StringProperty()

class LIST_OT_NewItem(Operator): 
    """Add a new item to the list."""
    bl_idname = "my_list.new_item" 
    bl_label = "Add a new item"

    list_name: StringProperty(name="list_name")

    def execute(self, context):
        item_list=eval("context.scene."+self.list_name+"_list")
        item_value=eval("context.scene."+self.list_name+"_item")
        item=item_list.add()
        item.name = str(item_value)
        return{'FINISHED'} 
        
class LIST_OT_DeleteListItem(Operator): 
    """Delete the selected item from the list."""
    bl_idname = "my_list.delete_list_item"
    bl_label = "Deletes an item"

    @classmethod
    def poll(cls, context):
#        item_list=eval("context.scene."+self.list_name+"_list")
#        print(bool(item_list))
        return True

    list_name: StringProperty(name="list_name")

    def execute(self, context):
        item_list=eval("context.scene."+self.list_name+"_list")
        index=eval("context.scene."+self.list_name+"_index")
        item_list.remove(index)
        index = min(max(0, index - 1), len(item_list) - 1)
        return{'FINISHED'}

class OBJECT_UL_List(bpy.types.UIList):

    def draw_item(self, context, layout, data, item, icon, active_data, active_propname):
        scene = data
        if self.layout_type in {'DEFAULT', 'COMPACT'}:
            layout.label(text=item.name)

class SCENE_PT_Params(bpy.types.Panel):
    """Creates a Panel in the scene context of the properties editor"""
    bl_label = "Define Properties"
    bl_idname = "SCENE_PT_def_props"
    bl_space_type = 'PROPERTIES'
    bl_region_type = 'WINDOW'
    bl_context = "scene"

    def draw(self, context):
        layout = self.layout
        scene = context.scene
        layout.label(text="Parameters:")
        split=layout.split()
        col = split.column()
        col.label(text="Parameter 1")
        col.template_list("OBJECT_UL_List", "",scene,"param1_list",scene,"param1_index")
        row=col.row()
        row.operator('my_list.delete_list_item', text='',icon='REMOVE').list_name="param1"
        row.operator('my_list.new_item', text='',icon='ADD').list_name="param1"
        row.prop(scene, "param1_item",text="units")

        col = split.column()
        col.label(text="Parameter 2")
        col.template_list("OBJECT_UL_List", "",scene,"param2_list",scene,"param2_index")
        row=col.row()
        row.operator('my_list.delete_list_item', text='', icon = 'REMOVE').list_name="param2"
        row.operator('my_list.new_item', text='', icon = 'ADD').list_name="param2"
        row.prop(scene, "param2_item",text="units")

classes = (OBJECT_UL_List,
        LIST_OT_NewItem,
        CustomListItem,
        LIST_OT_DeleteListItem,
        SCENE_PT_Params)

def register():
    for cls in classes:
        bpy.utils.register_class(cls)
    bpy.types.Scene.param1_list = CollectionProperty(type = CustomListItem)
    bpy.types.Scene.param1_index = IntProperty(name = "param1_index", default = 0)
    bpy.types.Scene.param1_item = FloatProperty(name = "param1_item", default = 500)
    bpy.types.Scene.param2_list = CollectionProperty(type = CustomListItem)
    bpy.types.Scene.param2_index = IntProperty(name = "param2_index", default = 0)
    bpy.types.Scene.param2_item = FloatProperty(name = "param2_item", default = 0.5)

def unregister():
    del bpy.types.Scene.param1_list
    del bpy.types.Scene.param1_index
    del bpy.types.Scene.param1_item
    del bpy.types.Scene.param2_item
    del bpy.types.Scene.param2_list
    del bpy.types.Scene.param2_index
    for cls in reversed(classes):
        bpy.utils.unregister_class(cls)

if __name__ == "__main__":
    register()

I wrote my code starting with the example here: https://sinestesia.co/blog/tutorials/using-uilists-in-blender/, and the example scrolls properly. I've compared the two codes and I do not understand why the example in the tutorial scrolls properly and mine does not. I would appreciate any suggestions.

Answer 1

In the col.template_list, I set the list_id parameter to "". In order for the scrollbar to work correctly, I needed to assign name to the list.