No doubt someone has already been here, done that, but I haven't seen it.
As you may know, there a couple of bugs with the Listpicker and it's indexing, namely that if you have duplicates in your Listpicker elements, the Listpicker always returns the index of the first occurrence, and if you use the Filter Bar this will alos return either an index of 1, or the first occurrence in the Listpicker elements. This workaround seeks to address these two issues.
Very simply, we add sequential numbering to all the elements going into the Listpicker, and then remove them again after picking, so the user is returned with just the element, and the correct index.
This also provides the added benefit of being able to filter the list by both the numbers and the elements.
In the video, you will see the index number shown in a label, this is the index number, not a truncation of the number shown in the list.
Here are the blocks
A short video as well :)
An aia file is attached if you want to extend this or just use it.