I noticed that my shepherd got stuck in whistling for a baby sheep for a long time, eventually when I checked back at her, everything was ok.
After some more time, she got stuck in that activity again. (screenshot)
She whistled way more than 20 times, until the baby sheep grow into an adult. Then everything was normal and working again as usual.
I do not know how she got in that state, and I do not have a save with that problem… The problem solved itself after some time.
But it was definitely bugged as she was trying to lure it into the farm, even though both were already inside it.