Hi! Have the same issue, but didn't understand what does it mean. Could you explain me briefly, please?

Great Kata! Thank you!
For those, who have difficulties passing tests, just be careful and attentive to the second condition of Kata:

• "only non-negative, single digit integers are allowed".
  It is too easy to miss the word "Single"
  Good luck!

test.assert_equals(filter_list([1,2,'aasf','1','123',123]) - in this list one of the digits "1" - is a string, not a number. So it doesn't show in results ([1,2,123]) not because it is a duplicate, but because it's a string. So you should check in your code if you have any "string" numbers and exclude them too.
You are welcome)