Essentiallink

The Essential mod used to be compatible with FancyMenu because of them adding support for FancyMenu from their side, but this compatibility seems to not be present anymore.

Since some update to their mod or launcher, users report massive problems again with Essential + FancyMenu, like Essential elements not being visible in the layout editor, or customized Essential elements reverting back to default when leaving the editor.

This GitHub issue talks about one of the problems.