Even before updating the new Animate CC, I've been experiencing some playback previewing problems.
When I hit return to preview the project within Animate, it plays at what seems like half speed. However, when I preview in the browser, it plays at the normal speed.
This is a big issue when trying to time things out. Anyone have a fix? I may have hit the wrong button along the way somewhere.
If you set your sound sync to Stream you can play from anywhere in the timeline, and you can scrub the timeline to check your timing. You only get Stream sync with AS3 documents, so make the animation as AS3, then when all of the timing is right you can convert the file to HTML5 Canvas, if that's what you need.
Inside Animate the UI has to keep everything updated, and so won't keep up with full frame rate if the animation is complex. A browser doesn't have to update quite as much, but, you might still get cases on slower machines where the sound and animation get out of sync. There are code solutions for that.
I’ve had this issue before and its ususally because of lack of memory on the compute. Try cleaning out junk files and close programs in the background. The more memory I’m your have, the better it’ll be. Also try using actionscript files, because you can set the sound to stream so that you can scrub along the timeline without having to restart each time if you have audio.