Properties not appear on the EXPOSED CUSTOM PROPERTIES panel

On 4.0
I create a properties on a sub component
On the main component, this propertie not appear both on QML and on the Properties panel

On my file exemple

Boost is the sub component 
Cluster is the main componant

On Boost, I create the propertie boostValue
An ArcItem and a time line bind on boostValue

On the Cluster component, I want to animate a time line base on the boostValue propertie
Chis propertie not exist 

I opened the same file on 3.9 and it's work well