Elemental block written to only one locale

Silverstripe Version: 4.11.0@stable
**tractorcow/silverstripe-fluent: 6.0
**dnadesign/silverstripe-elemental: 4.10

Hi all,

I have a SS4.7 website using Elemental Blocks and Fluent for two locales, all works well so far.
Now I tried to ugrade the site to SS4.13 but found that all pages (elemental blocks) have the same content, regardless of the locale.
I then set up a out-of-the-box installation with SS4.11, Fluent and Elemental, but this shows exactly the same behavior, content of language A gots overwritten by content of language B (or vice versa) when saving/publishing the blocks.
Any idea where to look for this issue? Did I miss to add a Fluent yml configuration? The SS4.7 site was done without any hacks or tricks …
Thanks for any hint on this!
If needed I can set up a test site to reproduce the error.

Best regards