Just in case, have you checked Library > Instruments > Klarinette (B) (in score) > Edit Instrument Name > Show Transposition (bottom of the dialog): it should be set to “Always” or to “Follow Layout Options”, maybe in your case it’s set to “Never”?
Thanks for the response, I checked this first, it’s set to “Follow Layout Options”.
And I can confirm that the settings of the horns are exactly the same.
I deleted also all custom text in the properties, no change.
Update: You pointed me in the right direction. After changing the option to Never and then back to Follow the transposition information magically appeared. Thanks a lot, much appreciated.