Language switch doesn't work on menu linked to "ALL" Language category

I have 3 languages on a site (DE, EN, FR). There is a menu item in each language (having their language set to EN, DE and FR), linking to the same category "products", which is set to "ALL" languages instead of having 3 language versions of the category. After upgrading the page to Joomla 4, that menu and all URL's below it are not routed correctly any more. 

Expected: 
URL in EN: /en/products
Switching to DE: /de/produkte
Switching to FR: /fr/produits

Actual behaviour: 
URL in EN: /en/products
Switching to DE: /en/produkte
Switching to FR: /en/produits

So the menu item alias in the URL does change, but not the language.
I tried setting the redirection "Use menu items" in flexicontent configuration to "with language 'ALL'", as well as "with language 'ALL' or with current UI language", but there was no difference in behaviour. 

Does any one have a clue how to still do the correct routing?
Thanks a lot!
Terry

hello do you have a direct link ?

For example here: www.barox.ch/en/products/ip-products
I have done a redirect on www.barox.ch/en/products/ to avoid that, but for all the pages below that menu it's still visible.
Here it's the same problem but less visible because the alias is the same for all languages:
www.barox.ch/support

It only happens there with the "All languages" category, all other items are fine.

Thanks for looking at it.

maybe its relevant to this ?
github.com/FLEXIcontent/flexicontent-cck/issues/1050

Not sure I get it - how do you think this is related?
There is no search involved and the types are also not obviously involved as it regards menu items with category display.

What does not behave like expected is probably the router, as there the SEF URL's (including the ones for language switch) are created. This does not appear for every menu item, only for the ones linking to a category that covers "all languages".