Ok, sorry I just found the answer in blog blog “night before Gutemberg”
⚠️ Position “high”
Due to major changes in the WP 5.0 post edit screen, the “high” position is no longer working. Field groups assigned to this position will not show in Gutenberg and we recommend changing these from “high” to “normal”.
We will look at solutions for this, but are unsure if it will be possible.
Hope you’ll find a way !!