There is a known bug with cows AI. I had same issue, too.
Please check if…
your barn is in a fenced/walled area
or cows went stuck on way home from field in a fenced/walled area (sometimes cows take a longer way home, just because there is a road)
Remove some single parts from your walls/fences to fix it. Make sure barn is outside of fenced/walled areas and make sure they don’t have gates or walled areas on their way home.