So This problem afaik only occurs in Unattended but,
Sometimes it clicks the button and sometimes it doesn't, but it doesn't throw an error because it can find the UI element.
See the example follows:

So the robot clicks on a button "DOWNLOAD DOCUMENT", which i have as a selector on only name "DOWNLOAD DOCUMENT"
But as you can see, one time it clicked on the button and saved the pdf file, the other time it also tried to click on the button, didn't throw an error that it coulnd't find the Button. But instead saved the page because it was unable to open the pdf file because in fact, it actually coulndt or didn't click the Button (even though it found the UI element).
I have also tried, move mouse to UI element and then click. Still works in attended but not in Unattended.
What can the solution be?
Note: pages of the site i try to automate load pretty slow, I have tried to work with more waits but it doesn't work in unattended yet.
@VJR, do you have any ideas?