I have a JC skill of 339 with trophy. I have just tried to make a Jewelers Glass Lens (50) out of 15 combines I have had 11 failures and 4 successes.
Not a bug, there some recipes, this is 1 of them, that is especially hard. Even if way above trivial. Look through old posts, if you can find it, and you see a dev has responded to this.
That one even has an inflated Fail chance. It's working as intended. You "grinding the lens" which takes time.
