I realize this is a year-old thread, but here's a solution in case anybody else has stumbled in here looking for an answer like I did:
PAD can't find the "Save as" button in the Edge downloads pane because the button is dynamic, and its attributes change each time it appears. In other words, it's not the same button each time. Your flow is looking for the button you clicked when you created the UI element, but that actual button no longer exists.
The solution is to edit out the attributes that change, so that your flow looks for something like the original button, but not the actual original button.
First, open the element for editing and go to "List Item 'What do you want to do...'" and uncheck the "Id" attribute. That digit on the end changes each time.
Next, go to "Button 'Save as More options'" and uncheck the "Class" attribute. The first value in that sequence changes each time.
Finally, go to "Button 'Save as'" at the bottom and uncheck the "Class" attribute there as well.
Disabling these three attributes worked for me, and I was then able to use the "Click UI element in window" to access it.
If unchecking these three doesn't work, create multiple instances of the element, then look at the Preview Selector at the bottom of each instance to see what changed. I had to copy all that mess from each one into Word to be able to compare them side by side to figure out what to uncheck.
