Hey @tatof, We are sorry you have had this experience and any inconveniences it may have caused. We are working diligently to make the major update we pushed a smooth transition. Unfortunately, some bugs along the way made it more difficult than it should have been.
We are about to make a patch for the shortcode converted (A bug caused this to be invisible at the moment). Once it is back live, it is a couple of clicks, and your shortcode should convert to the new method.
One of the reasons we lost the ability to make some features backward compatible was due to securing the plugin even further.
If you need any assistance we are always happy to help!
The SlickRemix Team
We just pushed an update to address the missing process on the front end on how to convert shortcodes. Thanks for bringing this to our attention. I can see how that would be really annoying. Hope you have a better day!