Why is a Level 50 culinarian failing Quick synthing maple surger?

[Inquisitor]

first off, i wanna ask same thing, but different situation, hempen yarn as a 50 weaver with careful synthesis 2 and full hq af gear fail 10% of the time

It doesn't matter what abilities you have when using quick synthesis. The game just uses standard synthesis repeatedly until the item is either finished or ruined. A 10% failure rate would be unusually high, but no individual person's experience is going to be a large enough sample size to demonstrate overall success rates. If you're getting a 10% fail rate you're just an unlucky outlier.

PS You can buy hempen yarn from a trade supplier for less than the value of the shards used during quick synthesis.