Can't send a Score to YouTube made in Musescore 3

Hello!
I'm now using Musescore 3 and uploaded a new score here on Musescore.com.
I wanted to upload the score also on YouTube, but there's no possibility to choose it.
In contrast to this, my older scores made with Ms.2 can be uploaded.
The button for sending it to YouTube only appears at the older scores from Ms.2.
Have got an idea?