Thinish thermoformed molds like these with large smooth surfaces often have issues with release marks.
Some discussion - https://forums.egullet.org/topic/98208-chocolate-molding/#comment-1645176
A bit more discussion - https://forums.egullet.org/topic/56184-chocolates-with-that-showroom-finish-2004-2011/?do=findComment&comment=1524966
Here's some further discussion you might find interesting - https://forums.egullet.org/topic/124257-polishing-chocolate/#comment-1670612
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