Hi,
from my limited Java knowledge, it seems that whatever way that the carpenter recipe registry or something similar somehow causes the KubeJS recipe server event to fail. I would be delighted to see this issue fixed.
Works even on a clean install with only Forestry and KubeJS installed.
MC ver: 1.20.1 w/ Forge 43.3.0

https://gist.github.com/carbonatek/a4864465769a6694a692d59c53831b1c

Thank you for your awesome work, and have a happy Christmas.
iCarbonZz_

P.S. Your mod brings me warmth and great nostalgia for something I used excessively in the past :-)

To add to this, if I execute /reload (the KubeJS way of sort of reloading the internal server - used for regenerating recipes) it leaves no errors and it works.
So, it has a temporary solution, but for those unaware, it breaks custom recipes because it simply breaks the loading sequence of KubeJS, so your custom recipes won't load until you reload.