Top righ position doesn't appear if window scrolled down

[csimpi]

Expected behavior

If I open a page and scroll down to the Save button, the alert should appear on the top right.

Actual behavior

If I scroll down, I can't see the log message.
If I click to the save to the bottom of the page, then I scroll up asap, I can see the alert (so this happens because it's hidden by scrolling)
If I scroll down, scroll up, and scroll down again, the log message appears well when I'm scrolled down also.

Steps to reproduce the behavior

Make a page that doesn't fit your viewport.
make a button that shows a success log message, and put it to the bottom of the page
Scroll down to the bottom
Reload the page
Click to Save

• you shouldn't see the log success message
  Click to Save and scroll up asap
• you should see the message
  Scroll down and click on the Save button again
• the message should appear well now

Version of Alertify in use

newest
+Windows 10, Chrome newest