Layout Editor of Component - Composite View Layout shows nothing

Dear KNIMErs,

while I tried to submit my personal solution to the next Just KNIME It Challenge, I found some strange thing and I wonder if it’s a bug or if I miss something substantial.

I have 2 Single Selection Widgets, a refresh button widget and a Bar Chart Node in my component and I simply cannot arrange them in the Composite View Layout of the Layout Editor.

See screenshots of my component and the layout editor:

Am I missing something? I was expecting to see the 3 ‘layoutable’ parts on the left hand side.

I use KNIME AP v 5.2.5 and have tried in both, modern and classic UI.

Thank you in advance for your kind help.