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When I use the brush tool, the border has some strange effects. I have no clue how to remove it. When I save the file, it all seems good, this only happens when I view it in Illustrator.

See image below

enter image description here

(I'm using Illustrator CC 2018 on a Surface Pro 4)

marked as duplicate by WELZ, Scott adobe-illustrator May 11 '18 at 20:13

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