Hi,
The ListView widget tends to need a tick or two before it’s fully refreshed after the underlying data changes; most changes to the source result in a call to STableViewBase::RequestLayoutRefresh, which schedules the refresh for the next tick. If you want to react to the actual size of the ListView, you’ll likely also need to schedule the resize for a frame (or two) in advance to be sure you’re getting an accurate DesiredSize.
Best,
Cody