Sorry, this appears to have already been reported and I missed it.

I'm not sure why, but enabling Cerys causes the following error in Factory Planner. I'll report the error over there as well.

The mod Factory Planner (2.0.16) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event factoryplanner::on_configuration_changed
factoryplanner/backend/handlers/generator_util.lua:46: attempt to index field '?' (a nil value)
stack traceback:
factoryplanner/backend/handlers/generator_util.lua:46: in function 'combine_identical_products'
factoryplanner/backend/handlers/generator_util.lua:110: in function 'format_recipe'
factoryplanner/backend/handlers/generator.lua:444: in function 'generate'
factoryplanner/backend/handlers/prototyper.lua:103: in function 'build'
factoryplanner/backend/init.lua:244: in function <factoryplanner/backend/init.lua:229>

https://github.com/ClaudeMetz/FactoryPlanner/issues/470
https://github.com/danielmartin0/Cerys-Moon-of-Fulgora/issues/21

Update: Even though Factory Planner does not yet have the fix pushed, Cerys is now compatible with it via a new checkbox setting called ‘Technology compatibility mode’.

what this setting do ? where find it ? on "startup" or "map" ?

In case anyone else wonders, it is a startup setting and it doesn't look like the fix is in factory planner for stable (yet, v2.0.16). So it is pretty nice to have this setting.