Schematics :
http://lectric-fx.com/wp-content/uploads/2015/07/FlintlockFlangerV1.2.pdf
Edit : I think I managed to fix it by changing the 2n5457's orientation (opposite from the pcb silkscreen).
I also added the modification I found here : https://www.madbeanpedals.com/forum/index.php?topic=31768.0
http://lectric-fx.com/wp-content/uploads/2015/07/FlintlockFlangerV1.2.pdf
Edit : I think I managed to fix it by changing the 2n5457's orientation (opposite from the pcb silkscreen).
I also added the modification I found here : https://www.madbeanpedals.com/forum/index.php?topic=31768.0