Hi Laurian Angelescu,
Thanks for reporting this!
It looks like the deferred scroll indicator. This is a tooltip-like element that should show only when deferred scroll is enabled and should contain information about the row coming in to view while scrolling.
Can you please let me know the exact version of the dlls you are testing with . Wi had such known issue long ago ( with an older version) .
The full XAML would be also helpful for us to reproduce the problem
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