When I insert a youtube video in the pro version and save everything is ok.
As soon I add any css-class to the video and save again, the editor will only recognize, that it's a media, but when I open it, all informations like url and class are not visible.
In the code, there is still written
<iframe width="560" height="315" src="/https://www.youtube-nocookie.com/embed/-AXvlsVppq0?rel=0" allowfullscreen="allowfullscreen" frameborder="0" class="embed-responsiv embed-responsiv-16by9"></iframe>
I hade the same results with version pro 2.6.32 and 2.6.33.
I use RS Firewall, but I think this time it's not the cause for the problem.
Using Firefox 62.0.3 (64-bit) unter Windows 10.