It used to work embedding youtube videos with the insert media button. But now it starts adding just https://www.youtube.com/embed/watch, the video id is completely missing.
I tried disabling the privacy enhanced mode and also the responsify plugin. 

what else could cause this?

It is strange, if I just paste the URL in the editor it works. If I click the "insert media" button and add the url this way, it does not work

perfect, thank you! It works again